Heroes 5.5 WarGame Edition - Tactical Edition.

You can still manage with a Griffin on level 4:D

Was the Griffin ever ranked higher? I remember it being lower, in the third game.:D
Out of all the creatures you listed, the Hydra is definitely out of place. Its rightful place is 7!!! and not with the Academy.
The rest, in reality, were new characters at the time of their creation. Well, the Centaur was in the third game, but it's not the same one anyway.