Riddlekeeper

A 1/4 Homunculus that taxes the act of attacking, not with damage but with cards off the top. Four toughness blunts most early aggression, and any creature that swings at you or a planeswalker you control pays two cards from its library for the privilege. The design tension is that this is punishment, not deterrence. Nothing stops the attack; the attacker still gets through if they want to, but every combat they declare grinds their deck two cards thinner. Against a go-wide board the accounting adds up fast, which is what makes the card read so differently depending on the table: as a defensive blocker it is unremarkable, but as the engine in a deck that wants opponents' libraries empty, the punishment becomes the plan. The mill happens on the attack declaration, before blocks or combat damage, so it fires whether or not the attacker connects and whether or not it survives the swing. That timing is the whole point: it converts the opponent's tempo into a cost they pay up front, turning their pressure into your win condition rather than just absorbing it.