If he is using Prankster he cannot use Poison Heal, unless you meant a teammate.you probably want to add poison heal on there, or recovery. also someone can switch into a resist/immunity of choice and pp stall
Or, I guess if you had like a Poison Heal:
Swampert-Mega @ Toxic Orb
Ability: Poison Heal
EVs: 252 HP / 252 Atk / 252 Def / 252 SpD
IVs: 0 Spe
- Dig / Thousand Waves
- Curse / Coil
Bounce works to inflict Paralysis while immune due to being Poisoned, Curse / Coil prevents Imposter from overpowering it like Swords Dance would.
Curse allows you to go second and underspeed Core Enforcer, while Coil patches up Accuracy issues on Bounce, etc.
The other moves gain STAB so they deal decent damage. Thousand Waves can prevent switching PP Stall while still gaining STAB.
Rayquaza-Mega @ Lagging Tail
EVs: 252 HP / 252 Atk / 252 Def / 252 SpA / 252 SpD
IVs: 0 Spe
- Swords Dance
You go last, due to the item, when you attack, but go first when you use Copycat to outspeed the foe.
Dig serves as a coverage move to hit the Rock, Steel, and Electric types that resist Flying moves.
Swords Dance makes sense so Dig and Bounce do decent damage, and so the foe doesn’t just spam Recover.
Lagging Tail can enable Bounce so you don’t have to worry about under speeding the opponent.
Lagging Tail also lets you underspeed Imposter when both of you are using the same move during the same turn.