In a fantasy novel, what animal sidekick character would you like to see?

[Sheena Halsberry]

I'm not looking for things like, white tigers or panthers or wolves. I'm more looking for characters like 'Puss in Boots' or 'Donkey' from Shrek, as well as 'Reepicheap' from Narnia.

And examples with how they could be humorous/useful?