Phyrexian Bloodstock

Color hosing folded into a body rather than a dedicated spell, this belongs to a multicolor-block tradition of creatures that punish a specific enemy color when they die. The trigger is the wrinkle that does the work: it fires on leaving the battlefield, not on entering or on attack, which puts the destruction on your schedule. Chump-block it, sacrifice it, bounce it, even let the opponent kill it, and a white creature dies, can't-be-regenerated and all. That makes the 3/3 awkward for any white creature deck to remove, since the cleanest answers (combat, a kill spell) just cash in the trigger. The "can't be regenerated" rider closes the obvious loophole: it was aimed at the white regenerators of its day, the defenders that would otherwise shrug off a death blow and survive to block again. As asymmetric hate it sits a tier below the era's hand-disruption and enchantment hosers, because it commits a five-mana body to a job that only pays off once. But the leaves-the-battlefield framing is the cleverest part of the build. The usual weakness of a hoser is that the opponent decides whether to engage it; here every route off the battlefield passes through the same target, so the destruction stops being a choice the opponent gets to make and becomes a tax on removing the creature at all.