Cannot be Normal Summoned if you control a Level 5 or higher monster. When this card is Normal Summoned: You can target 1 monster with 0 DEF in your Graveyard; Special Summon that target in face-up Defense Position. Its effects are negated. You cannot Special Summon any other monsters, except from the Extra Deck, during the turn you activate this effect.
You can revive a high attack monster with no defense. Then when your opponent attacks it use Gamushura to change your monster to attack position, ideally destroying your opponent’s monster and dealing massive damage in the process.
I remember this card being a nice tech in the TCG when Battlin´ Boxers were a meta deck. Thanks to King of Feral Imps, it was easily searchable along another staple of the deck (Kagetogake) and combined greatly with BB Glass Jaw (who has 0 DEF) to bring out a Synchro in a pinch. Guess that with a smaller Extra Deck in DL it won´t be that valuable, though.