Wurm's Tooth
Ninth Edition — uncommon
Artifact
Wurm's Tooth rulings:
2009-10-01: The ability triggers whenever any player, not just you, casts a green spell.
2009-10-01: If a player casts a green spell, Wurm’s Tooth’s ability triggers and is put on the stack on top of that spell. Wurm’s Tooth’s ability will resolve (causing you to gain 1 life) before the spell does.