Lim-Dûl's High Guard

The defining trick is the marriage of first strike to a repeatable regeneration cost, a combination that turns a 2/1 into a combat brick wall against ground creatures. First strike means the High Guard deals its damage before most attackers and blockers swing back; if anything survives to trade, the regeneration ability resets the body for the next exchange. Against creatures with two or fewer toughness that lack first strike themselves, the Guard wins the fight repeatedly so long as the black mana holds. The regeneration cost is the discipline that keeps the body honest: each save asks for mana that could otherwise develop the board, so a defensive turtle is a real opportunity cost rather than free permanence. It is also a clean expression of black's early skeleton template (a cheap body with a mana-fueled regenerate), and bolting first strike onto that template pushed the combat math without inflating the stat line. The weakness is built into the same wiring: regeneration replaces the destruction event, so it covers ordinary combat damage and most "destroy" removal as long as the mana holds, but anything that exiles, bounces, or sacrifices the creature routes around it entirely. The toughness of one is the other seam, since a -X/-X effect that lowers toughness to zero is not a destruction event and leaves nothing to regenerate. What you get is a creature that dominates a narrow band of combat math and folds the moment the opponent steps outside it.