((Steve Irwin has a really cool power. Do his mutations reset with each new form or do they accumulate and stack? Either way he's sure to get more powerful on longer missions as he accumulates more mutations or collects more specimens. What happens if he eats a non-human player character, does he gain their powers? The only one I can think of who is small enough to eat whole is Irene.))
((Damn you Square Cube Law!!!))
Of course, you can just tell physics to go [expletive] itself. If I can create a character who can call forth dolls out of thin air without requiring their equivalent in matter, then you can create your bug Aussie too!
((It's not really a question of physics but of game balance. Eating an ant then gettin +4 strength would just be OP. If anything eating an ant should mostly give fun esoteric bonuses like walking on walls, poison bite, burrowing ability, pheremone sense. Maybe extra limbs, or you shrink but retain your normal strength.
Any animals with flight would be good options. I'm surprised at how few flying characters this game has.))