10a pet that lights the tunnel
Most pets are decoration. This one throws off sparks that drift away and linger, so a fair amount of the space around you stays lit while you dig. It is not a replacement for torches, since the light wanders wherever the bunny wanders and the bunny is not calm, but on a mining trip it is free visibility for a slot you were not using for anything else. It also refuses to settle while you are on a wall or in the air, so expect it to be bouncing constantly during a climb.
getting it
The Zoologist puts it on the shelf once your bestiary is filled out to around the halfway mark, so it arrives as a reward for playing broadly rather than for beating anything specific. If you have been catching critters and killing one of everything you pass, it turns up without you aiming for it.
the joke
It is a yellow electric rodent whose dash is borrowed from a certain crossover fighting game, which is neither subtle nor meant to be. The tooltip is a pun welding static onto ecstatic.