Manahive

Equivalent emblems with a similar effect (opponent loses life, you gain life) in green/white/black (Ajani's colors) do not exist. Most emblems are unique. Closest card: Vraska, Betrayal’s Sting emblem (Whenever a creature deals combat damage to one of your opponents, they get two poison counters.).
Reason: Emblems are typically unique to each planeswalker and Ajani's is life drain, which is rare among emblems in those colors.