Toxic Nim

Pairing infect with a regeneration shield engineers an unusual kind of stubbornness, because the activated ability answers exactly the threat infect creatures hate most: damage-based removal. A black mana keeps this body alive through lethal combat damage and through effects that destroy, so it trades into blockers, absorbs incidental pings, and is back on the table to swing again. Regeneration replaces the destruction, so a 4/1 that "dies" to a blocker simply taps and stands up next turn. A board wipe built on destruction or burn (a Blasphemous Act, for instance) leaves it standing while the rest of the field clears. The fault line is the single point of toughness, because regeneration cannot raise it. Anything that gives -X/-X (a Languish, a Black Sun's Zenith) erases the creature before the shield ever gets a chance to fire, as does exile, as does a sweeper like Damnation that strips the regeneration option outright. The design walks that exact line: it shrugs off the destruction and the damage, then folds to the stat-lowering or shield-denying answer instead. The poison clock has its own ceiling. With no trample, a chump blocker eats the four power as -1/-1 counters and the defending player takes nothing; regeneration keeps the creature for next turn but cannot push poison through a wall. That makes this a grind threat rather than an evasive or explosive one, accumulating poison a turn at a time when the lane finally opens.