I know some parameters but how does it work excactly? Why is Aggron almost always in the selection?
Nobody knows. Nobody understand it.
Seriously now, it looks like bulkier pokemon that make little or no damage have always priority. It used to like Rhydon in the past, it currently likes Aggron. It likes making the fight the longest and ineffective possible. It never selects machamp against blissey because it assumes that we don't know how to dodge. Enemy pokemon in a gym that you are meant to fight the last, have priority in the selection...
Nobody likes the auto select.
It favors bulk over damage but it does also factor in the damage. Blissey never being autoselected, high level Espeons/Alakazams often being autoselected against Machamp raids, grass mons being autoselected over Kyogre against water type raids etc. are easy proofs that it also cares about you dealing damage.
I cannot find a counterexample to this. You may have just nailed it.
It is precisely why my groudon is selected vs Thunder Kyogre, Cloyster vs Blizzard Kyogre (4x ice resist and 300 def), aggrons vs flying rayquaza (4x flying resist and the high def), even though their quick moves may be left unresisted, or if they do any meaningful damage at all (looking at you, cloyster)
VS the usual gym suspects, I believe Aggron is the highest defense and 'usable' candidate that is resisting a DG Blissey, and also the 4x resist to hyper beam. This resist profile is almost uncontested elsewhere. Ttar might be chosen for double psychic blissey but you need to have the rest of the gym cooperate Ttar's resistances for it to be chosen too (but with 7 weaknesses, good luck with that)
A 4x weakness to fighting and ground by aggron is non critical- you don't see those in gyms other than the odd close combat from a non-fighting mon.
The autoselect favors survivability, starting with your highest CP. It loved Blissey for a while, until I can only assume after fan ridicule Niantic added an exclusion for Blissey. For the longest time it would ignore any pokemon that had any amount of damage taken, but I think that was eased a while ago. It favors Aggron now because it has high CP and a lot of type resistances, even though it lacks DPS.
Autoselect loves resistances and Aggron has many of them. It will heavily prioritize double resistances, then resistances and almost never suggest anything that's weak to both of the defender's moves. That's why we never see Machamp suggested against gyms, autoselect hates weaknesses.
Besides that there does seem to be some sort of damage calculation built in because in many situations high DPS counters will get suggested over tankier counters, like Espeons and Alakazams against Machamp over many other pokemon. There are also consistent differences between otherwise identical pokemon with different movesets which suggests that the game must be accounting for your damage potential in some way. An easy one where we can see it's flawed is B/SE Tyranitar being preferred over B/C against targets weak to dark, but not to rock. It looks to me like they calculate the raw DPS of moves, which would explain why it always favors fast high base power moves like Stone Edge, Hurricane, Hydro Pump, often incorrectly.
Honestly I think what they have is some sort of a simplistic TDO formula. That would explain why it sometimes gives Aggrons, sometimes faster counters that resist the defender and knows to suggest Raikou against water-types despite it having no resistances.
I've kept all my Rhydon and Aggron fainted so they are no longer selected. I'm over it.
Of course, Battle Parties have solved a lot of that issue for me. I can't believe more people don't create them. Despite the sheer number of people doing raids in my community, a disconcerting majority of them still don't understand counters or know they should be creating Battle Parties rather than be at the whim of the suboptimal auto-select.
Autoselect picks the "Bless" Pokémon for the task. They got this by taking the word "Best" and then ran it through Google Translate for every language they have Pokémon Go in. When they got to the end they translated that word back into English. So when you use Autoselect, you're using the Pokémon that you need to have a Blessing from the RNG gods to win with.
I’m not sure all of what it factors or the weightings.
The other day it autoselected a dodrio...Yes, I said dodrio....for a mewtwo raid in the wind as the first slot of my rejoin team.
It must seriously weight resistance and charge move because their is no reason for it to otherwise overlook unused quality gengar and ttar and maxed rayquaza (DtO in the wind!)
