I notices one of the most common suggested saying was,"This boss cheats." So, I'm not the only one that thinks that allowing bosses to using elements it doesn't have is wrong. Please, fix this problem.
It isn't a problem; it's the way the game is set up.
A "cheating"enemy is one who interrupts combat (plays out of turn) to cast a spell. For example, on the last floor of the Spiral Geographic (the "Warehouse") in Marleybone, if a player casts a healing spell, Knuckles McCloud will interrupt after that to cast a non-Absorb Rebirth. Then combat resumes with the next wizard or the enemy.
Enemies can cast spells outside of their school of magic, just as wizards can. The game is already ridiculously easy as it is and doesn't need to be "nerfed" anymore.