Big heads in K120 event:
Press L, R, L, R, L(2), R, L before the K120 event starts.
Big heads in K90 event:
Press R, L, R, L, R(2), L, R before the K90 event starts.
Big heads in Mogul event:
Press Up(2), Down(2), Left, Right, Left, Right, L, R before the Mogul event starts.