Pop Fizz: I want to see one of the upgrade paths make Beserker mode simply switchable(and also let you switch Beserker forms in the mode). I think it would help him a lot.
Ninjini: Nothing here.
Flashwing: I don't really have any creative ideas... As long as she gets flight, I guess.
Crusher: I just want to see the petrifying scream also freeze in Battle, otherwise he will probably the most useless Giant.
Chill: I'd like to see an upgrade that summons ice on the left and right sides as well as homing forwards. And I hope that the narwhals can be continuously summoned like

Thumpback: Anchor, dash, wave.
Hot Dog: I don't have many thoughts, but I hope the fire wave ends up larger. (Get your head out the gutter!

Hot Head: I'd like to see some form of flamethrower within his attacks.
Sprocket: Wrench for Melee, laser wrists, and... Hmm... I'm lost on a last attack.
Bouncer: No thoughts.
Fright Rider: As long as one of their attacks is lancing forward I'm okay.
Eye-Brawl: Punches and lasers and dashes, oh my!
Swarm: Maybe an upgrade that makes his "swarm" attack damage and another that increases its size.
Shroomboom: An upgrade that makes the richrocketing attack last longer and be controllable(so it sort of turns into a dash attack).
Tree Rex: ... I honestly can't think of anything interesting...