Invisible to the enemies until it's too late, Heavy Traps use a specialized trigger that only fires when the most powerful monsters step on it, but cause the splash damage to all nearby units. The splash also affects flying monsters, so Zafreeti + Project X + Heavy trap = KABOOM and everything dies. The triggering monsters are the Project X, Crabatron, D.A.V.E. and champions. The only monsters that can survive this are high level D.A.V.E.s and champions. After that any Zafreetis with them in range will heal them.