A team with large coverage

I guess 3 generalists should meet the criteria. For instance, SB Mewtwo, outrage Ray, MM Metagross.

I would personally suggest the following based on my experiences. I'm suggesting more than 3 so you can mix and match or prioritize some over others, depending on your resources:

• Latios (DB/DC) or Legacy Dragonite (DB/DC): A great generalist and potentially your lead attacker. DB has really good DPS, and DC can be used frequently. It can put a lot of pressure on opponents and cause them to burn shields early.

• Metagross (BP/MM): A strong overall generalist that has a combination of great bulk, quite a few resistances, and high damage output. It tears through Togekiss, Gardevoir, and Tyranitar with rock moves. It will also tear up future contenders like Mamoswine (though beware of ones running ground-type moves). Metagross is fairly popular though, so expect people to have counters (SB Mewtwo, Groudon, Entei/Moltres, or Tyranitar with dark moves).

• Mewtwo (PC/SB): If you're lucky enough to have one of these from EX raids or a trade, it performs well at the master tier. PC gains energy quickly, and SB hits hard even when its just doing neutral damage. Like Metagross, Mewtwo is a common sight, so people will likely have counters. It also shares Psychic-typing with Metagross and Latios, so you may not want to pick all 3 of them as you'd have too many shared weaknesses.

• Groudon (MS/EQ): I've really enjoyed Groudon at the Master Tier. Mud shot is one of the best quick moves in the game for EPS, so your charged moves will come frequently. It's also a hard counter to both Metagross and Tyranitar (who are both very popular in the meta) as well as Entei and Raikou (who aren't as popular but still see fairly frequent use). If you're ever able to save up and give it solar beam as a second charge move, it becomes even more amazing, as it can then outpace your opponent's Kyogre and beat it in a one-on-one match.

• Tyranitar (B/C): This is a popular counter to several heavy hitters in the Masters League such as Metagross, Mewtwo, Lugia, and Giratina. Bite has pretty slow energy gain, so crunch won't charge as fast as you might like, but bite has very strong DPS. So even as a generalist, Tyranitar will perform very well.

You must understand that doing this for master's league is practically impossible without second charge moves. Master's league meta is extremely narrow due to how powerful the top pokemon are, and there simply aren't many budget options at all.

Blamescott listed some very good options. Make sure that your entire team doesn't fall over to a single strong pokemon from the opponent. If you're bringing Groudon and Metagross without coverage moves, you're in trouble against a Kyogre, so make sure your third pokemon has a good matchup against it. Likewise if you have both Latios and Metagross, a single Mewtwo or Metagross with MM/EQ could sweep both if the opponent gets you to use your shields first. Etc. I'd suggest starting with Groudon and/or Latios because both are excellent in neutral matchups.

Zapdos, Metagross, Giratina. Depending on your situation you might want to replace anything but the Zapdos with a Groudon, Tyranitar or the Giratina with a Latios.

Do not use anything with Waterfall, Smack Down or Dragon Tail, they will wind up charged moves very slowly and will cause your downfall.

If it even comes, equip a Darkrai. Very few things in masters even have fairy, bug or fighting moves and it is fast enough to rip apart any Mewtwo before it can use Focus Blast. That should allow you to have 3 independent effectiveness profiles effectively.