Tristan, his golden variant and Bambi (Playable) are the only characters intended for being playable.
Expunged and Beta 1 - 1.0.2 3D Dave use the same sprite-sheet.
Bambi's origin is from a joke game called Marcello's Fun House.
The game is basically a Baldi's Basic's clone, however the game only has two rooms and Marcello (Bambi) usually kills you anyway.
In Polygonized and Furiosity, Dave is not actually angry, but instead needs help turning back to his "reality's form". From the Bambi update to the 1.0 update, Dave was furious as the name intended to be because you caused him to turn 3D.
Some characters in freeplay have a score multiplier for each notes, which means the player can get more/less score depending on what character they use.