Originally released as an April Fools joke disguised as a remake of GarchompMatt's Rotom character, Yee consists of both Peek and Oro; Peek does the singing and takes the hits while Oro does the interrupting and the attacking. Don't set M.U.G.E.N's difficulty to Hard 8 though—that'd be a catastrophYee.
Yee is a boss character that is controlled solely by the A.I. It only has one form of attack that involves Oro covering up a large portion of the screen while shouting "Yee!", acting as an unblockable full-screen attack that automatically activates at a set point during Peek's song, dealing 250 damage to the average character, K.O.ing them in only four hits.
Yee is horizontally bound to the centre of the screen and prevents the camera from moving left or right, which benefits the opponent more as it makes Yee (technically Peek) easier to hit. Yee has permanent Super Armour like most boss characters do, meaning it cannot be thrown or put into a custom state, though because there are no invincibility frames when it gets hit, multi-hit attacks (especially those that are able to hit on multiple frames, but can only hit the opponent once) are able to quickly overwhelm it.
Yee has varying difficulty levels, though what handles them depends on the version of Yee, with the default version (Yee.def) using the difficulty M.U.G.E.N is set to, and the WinMUGEN version (YeeWIN.def) using a customisable variable set in its Config.txt file. Regardless of which version is used, the difficulty level determines the interval at which Yee attacks, meaning at harder difficulties, Yee attacks more frequently, whereas at lower difficulties, it attacks less frequently; if the variable in WinMUGEN Yee's Config.txt is set to 0, Yee does nothing, allowing the opponent to freely attack it without ever getting attacked. If the difficulty level is set to Hard 8 or 8, Yee becomes invincible and the unblockable full-screen attack persists for the entire round until the opponent is K.O.'d, making Yee impossible to K.O. with regular characters.
This character is controlled solely by the A.I., so no activation methods are present.
The K.O. animation that plays when Yee has been defeated at least twice is identical to the special 'boss defeated' animation present in the Tankentai Sideview Battle System for RPG Maker VX, minus the wave effect.
If Yee is K.O.'d by a Hyper Attack after having been K.O.'d at least once prior, Dan Forden will show up in true Mortal Kombat 3 fashion and attempt to say "Toasty!" , only to be interrupted by Oro, producing "ToastYee!".
If the WinMUGEN version of Yee's A.I. variable is set to anything above 8, the behaviour defaults to that of level 4 difficulty.