Smoke

Smoke enters with two Utilitycounter.

Z9 Grenade ~{t}{b},remove an Utilitycounter:
Target opponent creates a Z9 Gas token.
(At the beginning of your upkeep. Z9 Gas put a
-1/-1 counter on each creature controlled by
this player. Vanishing ~4)

Smoke is an excellent chemist and biologist.
If you're wondering what's in these
grenades..... well, don't ask.