Doborog, remember my 2.1 comment on having classes? (here's the Link)
now is the best time to add something like that, cause you could add in robots with only some of the upgrades of these classes.
it would give the player some of that feeling of fighting something cool and unique.
there would be 2 levels of A.i. : normal and master. the master get all but the last of the 3 upgrades for the classes, forcing players to have to think about how they approach the situation and will help players develop varies advanced strategies for approaching enemies and levels(not TOO advanced, tho).
i also had another class idea: the berserker. this class wields an axe and is generally good at slaughtering hordes of enemies. his abilities are:
Smash: allows players to bring there axe down, temporarily stunning them for 4 seconds in a very short range. takes 2 energy to use.
Throw: grants the player access to laser throwing axes. these axes are only half the size of your normal axe, but cant be block by swords. takes 1.5 energy to use.
Execution: enemies that are stunned, on the ground, or have one leg, an animation where you either (its random), chop there metal head off, or chop there body in half going vertically. takes 2 energy per use.
anyone with a shield can block his normal axe and throwing axes. he can kill ninjas as long as he has Smash or throwing axes.
i really do hope you seriously consider these and some of the other ideas i other suggest.
Edit: the berserkers passive is that he recovers 10% faster from being unbalance and his axe swings 10% faster. he cant reflect projectiles, tho.