My idea would be for a ninja mouse, similar to the image I made here:
https://steempeak.com/art/@shaidon/ninja-mickey-something-for-scrawly-3
There are some copyright issues with this design, but I hope that it might spark a few ideas.
It appears you have a samurai looking character already.

Alternatively, a robot based on everyone's favourite sulphur crested cockatoo, @rustle would be interesting.
@rustle is a 'plushy' sulphur crested cockatoo modified to represent the Steem block-chain and shared around the world at Steem meet ups.

https://steemit.com/dtube/@steemsistershow/to0ohoe4
He's enshrined forever within the Steem community.

I even made a mock-up of a Steem Monsters card for him here:
https://steemit.com/steemmonsters/@shaidon/a-new-steem-monster-s-card

Even if these ideas are rejected, I hope that it sparks new ideas.

Do you have an idea of when we will be able to start playing the game itself? (Alpha stage?).