mtg slime against humanity commander deck not only fits the theme for this but also is going to be auto includes and be absolutely nasty! @wizards_magic is out here trying to break the card How To Build A Slime

A player with 10 poison counters loses the game

Something that both these and the before mentioned taxing effects have in common are that they give opponents a choice and doesn't force a condition on the game itself that is insurmountable

Paradox In Doctor Who , paradoxes range from relatively harmless to universe ending

Sazh Katzroy Sazh Katzroy is a guaranteed 2-for-1 that attacks as a 5/5 the turn after you play it

You'll pay the appropriate cost, and the spell will go on the stack as normal

One of Magic's best birds, Baleful Strix is the ultimate 2-for-1, drawing a card now and trading for something later, whether thats a removal spell or another creature