Unlock Lord of Chaos
Press Up, Up+Left, Left, Down+Left, Down, Trinagle+X at the character selection screen.
Unlock Minion of Choas
Press R1+ R2 + L1 + L2 + X + Up at the character selection screen
Unlock Minoon of Order
Press Up, Right, Down, Left, R1, R2, L2, L1 at the character selection screen
Unlock Strahd
Press Up, Right, Down, Left, R1, R2, L2, L1 at the character selection screen