Brostaligatr

A fusion of Speedy's Blastoise and Feraligatr. It is unknown how this fusion is possible, but both of Speedy's aces combined make for a terrifying, powerful foe.

They can fuse or unfuse whenever they want and there seems to be no penalty to doing this.
Damage received while in this form while persist after unfusing, splitting between the two Pokémon.
Knocking the fusion out will force them to unfuse, as they're unconcious and unable to fight.

This fusion has both of the aces mysterious abilities, rendering Electric attacks nigh futile and their physical attacks doing additional Water-type damage.

Wears shades because both Pokémon decided it was too cool to pass up, with Blastoise claiming he once saw a Squirtle wearing a similar pair.