Tier 1
The greatest defender in Pokemon GO is the same as it has been: Blissey. Even with the stat rebalance, the existence of Metagross, and the threat of multiple charge moves nothing is quite as potent as Blissey in Gym Defense.
Best Moveset: Zen Headbutt + Dazzling Gleam
Note: Almost any moveset is good on Blissey for one reason or another
Pros
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Hands down the greatest defender is all of Pokemon GO
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Only has 1 weakness
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Fast and charge moves optimize it against its single weakness
Cons
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Isn’t a Golden Razz Berry
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Isn’t a Party Hat Wurmple
Tier 2
Tier 2 Pokemon are the defensive elite. Their stats, resistances, and movepools allow them to handle most neutral threats and even punish their common counters. Their main drawback is that they need to have their motivation maintained to keep their performance which may be unreasonable for some.
Best Movesets: Dragon Tail + Dragon Claw or Outrage
Pros
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Unique defensive typing limits optimal counters to Fairy and Ice types
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Dragon-type counters may take heavy damage in defeating Dragonite
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Dragon-type STAB attacks are powerful and largely unresisted
Cons
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Countered so heavily by Ice-types that it may not be able to use its charge move
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Fairy-types both deal effective damage and have double resistance to Dragonite’s Dragon-type attacks
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Metagross doesn’t mind Dragonite’s attacks and can Meteor Mash through it
Best Moveset: Zen Headbutt + Meteor Mash
Pros
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Impressive bulk condemns neutral matchups to extended battle times
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Meteor Mash can put a large dent into anything that doesn’t resist it
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Zen Headbutt gives it an advantage over Machamp
Cons
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Handled well by Fire-type Pokemon
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Most relevant Charge Move is a Community Day exclusive attack
Best Movesets: Dragon Tail or Waterfall + Surf or Blizzard
Pros
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Impressive bulk condemns neutral matchups to extended battle times
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Powerful, diverse moves keep it threatening even to its more optimized matchups
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More or less all the best parts of Lapras, Vaporeon, and Gyarados rolled into a magnificent Pokemon
Cons
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Becomes less threatening once moveset is figured out
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Despite its performance, its defensive-typing doesn’t cause many switches
Best Movesets: Dragon Tail + Dragon Claw or Outrage
Pros
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Unique defensive typing limits optimal counters to Fairy and Ice types
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Dragon-type counters may take heavy damage in defeating Dragonite
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Dragon-type STAB attacks are powerful and largely unresisted
Cons
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Countered so heavily by Ice-types that it may not be able to use its charge move
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Fairy-types both deal effective damage and have double resistance to Dragonite’s Dragon-type attacks
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Metagross doesn’t mind Dragonite’s attacks and can Meteor Mash through it
Best Movesets: Dragon Tail or Waterfall + Surf or Blizzard
Pros
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Impressive bulk condemns neutral matchups to extended battle times
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Powerful, diverse moves keep it threatening even to its more optimized matchups
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More or less all the best parts of Lapras, Vaporeon, and Gyarados rolled into a magnificent Pokemon
Cons
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Becomes less threatening once moveset is figured out
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Despite its performance, its defensive-typing doesn’t cause many switches
Tier 2.5
Tier 2.5 Pokemon are not as potent as tier 2, but are arguably more practical to use due to their blended resistances or CP-range performance.
Best Moveset: Waterfall or Dragon Tail + Hydro Pump, Crunch, or Outrage
Note: Almost any charge move is fine on Gyarados for one reason or another
Note: May actually benefit from having 2 Charge Moves, unlike most other defenders. Hydro Pump is great, but actually using a Charge Move is even cooler.
Pros
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Unique defensive typing limits optimal counters to Electric-type Pokemon
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Resists both Machamp and Metagross
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Powerful Hydro Pump could potentially knock out would-be Electric-type counters
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Crunch and Outrage give it an additional threat to Psychic and Dragon-type Pokemon respectively
Cons
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Countered so heavily by Electric-types that it may not be able to use its charge move
Best Movesets: Confusion + Shadow Ball, Psyshock, or Focus Blast
Note: Almost any charge move is fine on Hypno for one reason or another
Pros
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Confusion is of the most powerful fast moves for defense
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Shadow Ball gives Mewtwo and Metagross reason to be wary
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Excellent performance at lower CP levels
Cons
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Dominated by Metagross, Mewtwo, and Tyranitar
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Best charge moves are legacy
Best Movesets: Confusion + Any
Pros
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Impressive bulk and low CP range makes Slowbro optimal for both gym-height and long-term gym defense strategies
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Confusion is of the most powerful fast moves for defense
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Resists both Machamp and Metagross
Cons
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Dominated by Tyranitar and Mewtwo
Best Movesets: Confusion + Any
Pros
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Impressive bulk and low CP range makes Slowbro optimal for both gym-height and long-term gym defense strategies
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Confusion is of the most powerful fast moves for defense
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Resists both Machamp and Metagross
Cons
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Dominated by Tyranitar and Mewtwo
Best Movesets: Confusion + Any
Pros
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Impressive bulk and low CP range makes Slowking optimal for both gym-height and long-term gym defense strategies
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Confusion is of the most powerful fast moves for defense
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Resists both Machamp and Metagross
Cons
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Dominated by Tyranitar and Mewtwo
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Only has access to single bar charge moves
Best Movesets: Iron Tail or Dragon Tail + Heavy Slam or Crunch
Pros
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Impressive bulk and low CP range makes Steelix optimal for both gym-height and long-term gym defense strategies
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Overall a powerful matchup against Metagross, Dragon-type Pokemon, Mewtwo, Tyranitar, and Electric-type Pokemon
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Compliments other defenders well potentiating the opponent having to switch often throughout the gym battle
Cons
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Has a wide variety of optimal counters in Fighting, Fire, and Water-type Pokemon
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Machamp says “Hi”
Tier 3
Tier 3 Pokemon are excellent gym defenders that would rate higher on a more generalized defender tier list but are ultimately held back due to their weakness to Machamp and lack of threat towards Metagross.
Best Moveset: Zen Headbutt + Dazzling Gleam
Note: Almost any moveset is good on Chansey for one reason or another
Pros
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Like Blissey in every way but with significantly lower Attack and Defense
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Its low CP gives it a slower motivation decay rate, allowing it to outperform Blissey over time
Cons
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Negatively impacts the gym-height strat, having a max CP below 1950
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Most attackers will just plow through it without fear of Chansey’s abysmal damage output
Best Movesets: Thunder Shock + Thunderbolt or Rock Slide
Pros
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Impressive bulk condemns neutral matchups to extended battle times
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Resists Metagross and Dragon-type attackers
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Rock Slide covers its Fire-type weakness
Cons
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Is weak to Machamp and doesn’t do much to threaten it
Best Moveset: Yawn + Play Rough
Pros
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Extremely high CP cap can optimize even uncoordinated gyms for the gym-height strat
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Can cause several of the opponent’s Pokemon to faint with the hard-to-dodge charge move, Play Rough
Cons
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Performance is dependent on being high level, highly motivated, and using Play Rough
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Has potential to do nearly no damage to an opponent due to Yawn
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Metagross doesn’t care about Play Rough
Best Moveset: Zen Headbutt + Body Slam
Note: Heavy Slam is a decent alternative
Pros
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Very strong defender, with a high base stats and only 1 weakness
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Can be very punishing with its charge move Body Slam
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Its level 20 raid catch/egg hatch CP range makes it a low investment option for “gym height” and “low CP decay” synergistic strategies.
Cons
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Machamp and Metagross say “Hi”
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Best charge move is legacy locked
Tier 3.5
Tier 3.5 Pokemon are optimal at countering several top defenders, but fall flat against many others. If a gym has a glaring weakness to the Pokemon types they perform well against, it could be worth slotting them in.
Best Movesets: Fire Spin or Air Slash + Blast Burn
Pros
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Resists both Machamp and Metagross
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Can deal massive damage with Blast Burn
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Is freaking Charizard
Cons
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Almost as vulnerable to Electric-type damage as Gyarados is
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Handled easily by Water, Rock, and Dragon-type Pokemon
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Best charge move is a Community Day exclusive move
Best Movesets: Confusion +Earth Power, Mud Slap+ Psychic
Pros
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Resists Machamp, threatens Metagross, and resists Electric-type damage
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Its low CP gives it a slower motivation decay rate, allowing it to outperform many defenders over time
Cons
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Low damage output makes it susceptible to neutral attackers
Best Moveset: Counter + Play Rough
Pros
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Can cause as many switches as Steelix but has fewer weaknesses
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Threatens Dragon, Dark, and Fighting-type attackers with Play Rough
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Ground-typing may make Metagross users wary
Cons
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Most optimal moveset is predictable and does poorly against Water and Grass counters
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Less CP range utility than Steelix
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Doesn’t resist Metagross or Dragon-type attackers like Steelix does
Best Movesets: Waterfall or Metal Claw + Hydro Pump or Blizzard
Pros
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The greatest defender against Metagross
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Performs well against Dragon-type attackers
Cons
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Vulnerable to Machamp and Electric-type attackers
Best Movesets: Confusion + Dazzling Gleam or Shadow Ball
Pros
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Fairy-typing provides resistances to Fighting- and Dragon-type Pokemon
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Confusion is of the most powerful fast moves for defense
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Counter coverage to its more optimized counters through charge moves
Cons
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Quickly subdued by neutral threats
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Metagross says “Hi”
Best Moveset: Counter + Play Rough
Pros
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Can cause as many switches as Steelix but has fewer weaknesses
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Threatens Dragon, Dark, and Fighting-type attackers with Play Rough
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Ground-typing may make Metagross users wary
Cons
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Most optimal moveset is predictable and does poorly against Water and Grass counters
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Less CP range utility than Steelix
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Doesn’t resist Metagross or Dragon-type attackers like Steelix does
Best Movesets: Waterfall or Metal Claw + Hydro Pump or Blizzard
Pros
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The greatest defender against Metagross
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Performs well against Dragon-type attackers
Cons
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Vulnerable to Machamp and Electric-type attackers
Best Movesets: Hidden Power or Air Slash + Dazzling Gleam or Aerial Ace
Pros
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Fairy-typing provides resistances to Fighting- and Dragon-type Pokemon
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Noticeably more tanky than Gardevoir against neutral threats
Cons
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Flying-type invites Electric, Ice, and Rock-type attackers
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Metagross says “Hi”
About the Tier List
This Tier List was formulated after the Fall Stat Rebalance and before the PvP teasers. Where the (slightly outdated) specific defender tier lists aim to highlight the best defenders for different defense strategies, this tier list rates which Pokemon are generally the best to invest in on defense. If you’re familiar with motivation decay ranges, you can easily pick out which defenders would excel under which specific strategies.
It is important to note that gym defense isn’t so important that you should be investing your last stardust into defense Pokemon. Golden Razz Berries will do more to stop attackers than most Pokemon will with their native stats. However, it is apart of our due diligence to keep players informed of the best defenders in Pokemon GO!
Methodology
For the quantitative side of this model, simulations were performed using GoBattleSim with the 5 most relevant gym attackers in the game: Machamp, Metagross, Raikou, Rayquaza, and Shadow Ball Mewtwo. These simulations used level 40 and 2000 CP defenders against the aforementioned attackers at level 40, both with and without dodging specials. The initial rankings were based on these defenders sorted by their time to KO combined with their lethality.
Battle times were adjusted for unfavorable offensive matchups. Adjusted battle times were replaced with either Machamp or Metagross’s battle time plus 5 seconds. In the event the matchup was unfavorable for both Machamp and Metagross, the most appropriate attacker’s battle time was chosen plus 10 seconds. From here, rankings were re-sorted and a weight was given to Pokemon that performed better against Machamp and Metagross even with the adjusted rankings.
For the qualitative side of the model, defenders were further adjusted for their resistances, CP-range performance, and overall usefulness in practice. Spot simulations were also performed for some defenders against specific threats outside of the 5 selected attackers. In doing so, it was found that several specific qualities separated defenders not named “Blissey”: How practical they are, if they’re weak to Machamp or not, and if they only perform well in a handful of specific matchups. How important these qualities are is what then defined the tiers.
Overall, while it cannot be argued that Blissey is clearly Tier 1, most other defenders highlighted could be valued higher or lower than presented here. For example, Tier 2.5 Pokemon arguably have more practical applications than Tier 2 Pokemon despite being worse in performance overall. Tier 3 Pokemon defend very well against most Pokemon not named “Machamp” and Tier 4 Pokemon can perform as well if not better than Blissey in their favorable matchups.
The Future
Now that PvP is out, Pokemon can have two charge moves to pick from instead of just one. This is a huge advantage for some attackers and may give a slight edge to some defenders, but overall doesn’t affect these rankings much at all. It’s not that Heavy Slam won’t help Machamp overcome Fairy-type Pokemon, it’s that swapping to Metagross or another attacker will still be a better option. On top of that, most Pokemon don’t get attacks that help significantly with their poor matchups, and if they do, they’re often single bar Charge Moves. For example, Raikou, Zapdos, and Electivire’s movepool “expansion” doesn’t mean anything for them on gym offense.
For dedicated gym defenders, you will likely want to stick with one charge move. Reports indicate that charge move selection from gym defenders is random; therefore any niche advantage in giving Milotic both Surf and Blizzard (for example) could turn back on you as a disadvantage. In short, its a steep stardust investment with nebulous results. At best you'll make the attacker audibly state "Oh, they have two charge moves" as they proceed to knock you out of the gym, but most probably won't even notice.
If gym defense adopted the new energy and damage boost system PvP appears to have, then things could change quite a lot. Removing animation time, and completely changing the damage and energy requirements for attacks would obviously alter what's good by a great deal. We’ll have to see what the future brings and update then!