Other known variants
x2Poison Peak
During Pokémon Checkup, put 2 more damage counters on your opponent's Poisoned Pokémon.
Poison JabYour opponent's Active Pokémon is now Poisoned.
Because of Sneasler’s virulent poison and daunting physical prowess, no other species could hope to best it on the frozen highlands. Preferring solitude, this species does not form packs.
Does a poisoned Fusion Strike Pokemon with Fusion Strike Energy attached take additional damage counters from Radiant Hisuian Sneasler's "Poison Peak" Ability?
No, because Poison Peak is an Ability and Fusion Strike Energy prevents all effects of your opponent's Pokemon's Abilities.
If I use Drapion VSTAR's "Hazard Star" VSTAR Ability to poison my opponent's Pokemon with 3 damage counters during Pokemon Checkup, and I have Radiant Hisuian Sneasler with the "Poison Peak" Ability in play, does my opponent put 3 or 5 damage counters on their poisoned Pokemon during checkup?
Five damage counters. Poison Peak adds 2 damage counters to whatever the current number of damage counters are being placed for poison.