Now, I'm going to say something pretty controversial, MGG it's a good game (a pretty good one, in fact), but it's not a hard one.

Let me put you in a situation:
Your opponent has a Cyber mutant, a Necro and a Zoomorph, what do you do? Obviously send in your strongest Galactic, your strongest Mythic and your strongest Cyber.

What I suggest? Make some mutatnts gain specific bonus when they are with other specific mutants.
The most Obvious example that I can think of are The Experiment and Britany, since Brritany was made specifically to make The Experiment fall in love, if you have both of them, they gain an attack bonus, or a life bonus, or some other knd of bonus.
Like I said, those two are the most obvious example, but other "combos" could be Nordic Knightmare, Valkyrie and Thor. Or Eva, Darwin and Neo-Urban XIII. Maybe even Nebulus and the 12 zodiac Mutants, that would make them see more play again.
I think that this mechanic would make older, less used mutants, be used again, and sperk new life into the teams of the players.

Anyway, those are just my opinions.
(Plz reply and leave your suggestions, that way Celsius Online will put this into the game).