Defiant Bloodlord

The lifegain-to-drain conversion existed long before this Vampire wore the crown: Sanguine Bond turned every point you gained into a point an opponent lost, and this is that engine bolted onto a flying body. The redundancy matters more than the rate. Pair either with Exquisite Blood (which gains you life whenever an opponent loses it) and the loop runs until someone is dead, a two-card combo that mono-black drain decks have leaned on for years. On its own it is a slow clock with a steep tax: a 4/5 for seven that produces no drain by itself, since the trigger is parasitic and needs a lifegain density the rest of your deck has to supply, whether through incidental gains, dedicated lifelink, or sweeping symmetrical gain. That is the design tension: the drain is only as strong as the lifegain feeding it, and the card asks you to build that source elsewhere. The flying keyword is the quiet justification for the body, giving you a finisher that can actually pressure life totals while the trigger grinds away underneath. What separates it from Sanguine Bond is that it attacks: where the enchantment is pure engine, this is an engine that also flies in for four and threatens to close the game whether or not the combo assembles.