Small Key



The Small Key is featured in many Zelda games. It can be found in small chests and by killing enemies, such as Rats In A Link to the Past, but could actually be bought in LoZ. A Small Key can be used to open locked doors that have chains around them. In every Zelda game, except LoZ, they can only be used in the dungeon where they're found.

They have appeared in every single mainstream Zelda game to date and there is little chance that this will change anytime soon.