1. DCCC- If you beat the coure twice you unlock a secret blue stage which is a lot HARDER!!!
2. TNC- after beating the boss throw stars at the talking computer (can't remember her name) and you move on to a harder level
3. LGM- I just played it A LOT and unlocked two secret levels
If you know any other Nintendo unlockables please share with everyone else.
P.S I'm on my Wii U
