If you control a Level 4 or lower EARTH Rock-Type monster: You can target 1 Level 4 or lower "Magnet Warrior" monster in your Graveyard; Special Summon it. You can only use this effect of "Magnetic Field" once per turn. Once per turn, at the end of the Damage Step, when an EARTH Rock-Type monster you control battled an opponent's monster, but the opponent's monster was not destroyed by the battle: You can return that opponent's monster to the hand.