This set sounds good?
Pinsir-Mega @ Leftovers/Sharp Beak
Ability: Aerilate
EVs: 252 HP / 252 Atk / 252 Def / 252 SAtk / 252 SDef / 252 Spd
Adamant Nature
- Belly Drum
- Extreme Speed
- Megahorn
- Drain Punch
This set is a high risk high reward set. If the speed tie is won against a full HP Imposter Chansey with Eviolite switch in, then it can pull the OHKO with ExtremeSpeed.
+6 252+ Atk Aerilate Mega Pinsir Extreme Speed vs. +1 252 HP (Base 250 HP) / 252 Def Mega Pinsir: 788-930 (111.9 - 132.1%) -- guaranteed OHKO
This is of course assuming you can pull that Belly Drum off, which could be difficult to pull off and survive a hit. Now if it can be pulled off, since Drain Punch isn't a very reliable source of recovery, this is pretty much a one shot deal. So I'd recommend that either the opponet is asleep, or you have a sub up before attempting the sweep.
Also, hazards are going to be highly recommended before using this because if you come in, pull off the Belly Drum, and they switch into Sturdy Shedinja, that Pinsir set has nothing to hurt Shedinja and nothing to regain HP, because Drain Punch will recover 0% against Shedinja. This means that M-Pinsir will need to be switched out and won't be able to pull off any more Belly Drums.
I'd recommend if you want to improve this set, change out Megahorn for Leech Seed or Infestation to take down the bug, and replace Belly Drum with Swords Dance. Though if this happens then M-Pinsir can no longer have a chance to OHKO a full HP Imposter, that pink blob can even survive a crit it looks like.
+2 252+ Atk Aerilate Mega Pinsir Extreme Speed vs. +1 252 HP / 252 Def Mega Pinsir: 396-468 (56.2 - 66.4%) -- guaranteed 2HKO
There's also Ho-Oh, Mega Aerodactyl, Megazard-Y, and Landorous-T too.
There's something that all those Pokemon lack, they aren't as beast as Pinsir. :D