The Wing Cap is an item found in Super Mario 64. When wearing a Wing Cap, Mario becomes Wing Mario and has the ability to fly. Mario can perform a Triple Jump or be shot from a cannon and begin flying. To obtain the item, Mario must find a red ! Block and hit it. A Wing Cap will then pop out of the ! Block.
As a collectible item, the Wing Cap itself was largely omitted from Super Mario 64 DS, which replaced it with a single feather from the cap's wings (referred to as simply "Wings"); however, the Wing Cap was still granted upon obtaining this item. Only Mario could use Wings, which gave him identical abilities to those seen in Super Mario 64; if another character struck a box containing Wings, they would simply earn a Power Flower. However, a lone, traditional-style Wing Cap could be found in one of the game's multiplayer stages; if Yoshi (who, along with other members of his kind, was the only playable character in multiplayer mode) put on a Wario or Luigi cap, he could use this Wing Cap, again differing it from the Feather. Yoshi can even use it without the caps and grow wings on his body, similar to the blue shell in Super Mario World. It is possible that this one Wing Cap and its strange mechanics were added simply to make the concept of characters flying in multiplayer mode more fair for the mode in question; however, it may have also been a sort of remnant of beta programming stages where all (or at least most) characters could fly with the Wing Cap. (Indeed, an early promotional video of Super Mario 64 DS, then called Super Mario 64x4, did depict all four characters under the effects of an unseen Wing Cap, possibly the aforementioned Wings.)
There is also a Wing Cap on the roof of Princess Peach's Castle. When Mario earns all 120 Power Stars, a cannon will allow him to easily access the roof, however the roof is accessible at any time by other, much harder means.