Skithiryx, the Blight Dragon

Ten poison counters end a game, and a 4/4 flyer with infect deals four of them per connection: three swings, and the clock runs out of road. This is the threat that made poison a real win condition rather than a number on the back of the life-total card nobody crossed. The two black-mana abilities exist to guarantee those swings happen on your terms. Haste means the count starts the turn it lands, no summoning-sickness window for the opponent to exploit. Regeneration walks it through the destruction-based removal that would otherwise interrupt the assault, the qualifier being that regeneration replaces destruction and nothing else: an edict, an exile, or a -X/-X effect still kills it clean. Stack the protections it does have and the dragon resists the standard answers to a poison plan: flying dodges chump blockers, regeneration absorbs targeted destruction and most sweepers, haste denies the defender a turn to set up. And every poison counter it lands sticks to the player it hit: kill the dragon and the counters stay, because poison sits on the opponent, not on its source, and a player's poison total only goes one direction. The discipline is that none of the protection is free: each activation drinks the same black mana you would otherwise spend developing a board, so the dragon punishes sloppy racing even as it rewards racing at all. It remains the most self-sufficient infect finisher printed, a one-card clock that demands no supporting cast to function.