Skitters
Prince
One thing is, I've noticed if you give a unit double speed in a terrain type, they tend to not be in that terrain much because they are capable of moving through and out! So if you give them double forest speed, you will always find them on a bare tundra hill.
I was actually toying with the idea of a gorilla advancement line! Semi-civilized gorillas.
Out of interest - if an AI unit has a promotion that gives them a combat bonus in a certain terrain, does it encourage the AI to keep the unit in that terrain? So for example if Gorilla's and Tigers had a bonus for being in the jungle would it encourage the AI to keep it there?