World Legacy - "World Key"

You can discard 1 "World Legacy" card; you can Tribute Summon 1 monster during your Main Phase this turn, in addition to your Normal Summon/Set. (You can only gain this effect once per turn.) At the start of the Damage Step, if this card battles an opponent's Link Monster: You can return that monster to the Extra Deck. You can only use each effect of "World Legacy - "World Key"" once per turn.