Kassim, Sotseka Naturalist

Other Naga you control get +1/+1.
Whenever a -1/-1 is put on a creature an opponent controls, add {b} or {g} to your mana pool. Until end of turn, this mana doesn't empty from your mana pool as steps and phases end. When this mana is emptied from your mana pool, you gain 1 life for each mana that left your mana pool this way.