New mobs in FTB Naturally spawn?

[Karver]

The new mobs in FTB do they naturally spawn? Or do you have to spawn them like the wither. How do you spawn them legit? And if they naturally spawn whats the chance they will spawn because i havent seen any of them.

 

[WTFFFS]

The only mod I can think of that spawns "new mobs" in FTB is the Twilight Forest mod and I believe you have to go to the TF dimension to see them.