Enduring Tenacity 
Enchantment Creature — Snake Glimmer
Whenever you gain life, target opponent loses that much life. When Enduring Tenacity dies, if it was a creature, return it to the battlefield under its owner's control. It's an enchantment. (It's not a creature.)
Legality
standardLEGALpioneerLEGALmodernLEGALlegacyLEGALvintageLEGALcommanderLEGAL