Huge power/Pure Power obtainers:
Greninja: NO
Talonflame: NOPE
Bellosom: 80 atk not bad
Sudowoodo: 100 y'all
Sableye: 85 atk not bad
Aggron: Nope. Nope.
Manectric: God that's fast. No thanks.
At least half of the obtainers would be stupid strong, AND fast. Azumarill's allready top OU with 50 atk and no speed worth talking about. I think we can safely ban the ability overall from everything that doesn't naturally get it unless you really want to see Sudowoodo running around with stone edge of the gods.
Perhaps some initial quick bans, and a testing period for the weaker mons, at the very least.
Azumarill also has good HP, an excellent typing, STAB priority of an excellent type, and Belly Drum. That's a misleading comparison. Medicham has
60 Attack and better Speed, but until Mega Medicham came along nobody cared that much.
Greninja: Got banned from Ability Shift, although it took a while. On the other hand
everything is powered up in Mergemons, so I'm not remotely convinced it's actually ban-worthy.
Talonflame: Has to give up priority, keep in mind. Quick Attack from Diggersby is not a replacement for Gale Wings Brave Bird, and Vivillon's movepool is not exactly an amazing boost for it. Quiver Dance is nice, but not synergistic with Huge Power.
Bellossom: On its
own it only gets Leaf Blade and Drain Punch, which is a bit meh. However, it's getting Azumarill's movepool (So it can do the Belly Drum sweep, only it has more Attack) and also Ampharos' movepool, which actually adds a surprising amount of coverage, not to mention Cotton Guard.
Sudowoodo: Oh god it already has Sucker Punch innately.
Sableye: Its base attack is
75, not 85. Double-strength Foul Play that it gets STAB on (Yes I know Huge Power claims to double
Attack but it still boosts the user's Foul Play), gets STAB Sucker Punch from Mawile (And Delcatty, actually), can already heal itself, has a superpowerful Fake Out... oh, and it gets Cosmic Power too, because Delcatty has it. So run a defensive Sableye with Cosmic Power and double-strength Foul Plays, as one possibility.
Aggron: I agree, mostly because it gets
both Mawile's movepool
and Medicham's movepool -so Swords Dance, Sucker Punch, and Bullet Punch are all within its grasp, meaning it doesn't even need to Rock Polish -it can just Swords Dance and start the murder. Or you can Rock Polish and go for the Head Smash sweep, either way.
Manectric: Ir gets Medicham's movepool and... Plusle's. 75 Attack is better than, say, Azumarill, and it has actual Speed, but Electric moves are crap Physically if you're not Zekrom, Kyurem, or Pikachu, and it's still going to be painfully fragile. I'm not that scared of it.