Creatures with this ability don't grant poison counters but they wither them away when they deal damage to another creature, adding -1/-1 counters instead of dealing damage
That's because Pokemon Sword & Shield, with their dominant gameplay gimmick being Dynamax and Gigantamax, gave the TCG's creators the chance to introduce V, VMAX, and (to a slimmer extent) V-UNION
The draft environment is all about playing to the board, so you need to prioritize good creatures and better removal
On the other hand, I dont put too many details into the background, leaving a bit to the imagination and making the Pokmon pop
Overall, I really do like the idea of this deck
As for aggro payoffs, Rune-Brand Juggler, Deadly Complication and Clandestine Meddler are all pretty decent