Marrow Bats

A 4/1 flyer that refuses to stay dead, but the price is steep enough to make you feel each refusal. Regeneration normally costs mana, which means a creature with a regeneration shield taxes your turn twice: once to play, once to protect. This bat pays in life instead, four points at a clip, which untethers the ability from your mana entirely. The skeleton can block, soak a removal spell, eat a combat trade, and come back swinging as many times as your life total can stomach. That last clause is the constraint doing its work: with only one toughness on the body, the card is built around a fragile frame that the regeneration is meant to paper over, and the life payment turns durability into a slow self-burn. Against decks that pressure your life total, the resilience evaporates; against grindy attrition, four life a turn buys an evasive clock that opponents cannot kill conventionally. The design belongs to the old school of thinking that treats life as a spendable resource, sized so the body is just good enough to be worth defending and just flimsy enough that you keep being asked the question.