The Adventures of Cookie and Cream definitely qualifies.
I like this thread. I'll try: Top-down Cooperative Games That Go Horribly Wrong And Destroy Friendships
Magicka 1, and I assume Magicka 2:
Space Griffon VF-9
Also, Japanese dungeon crawling shooters set in some sort of robotic suit
Iron Angel of the Apocalypse (and sequel)
Kileak: The DNA Imperatives (and sequels) (only noticed it was in the quoted post after the fact, doh. Though it's worth noting Brahma Force is a spiritual sequel to Kileak)
Rengoku Tower of Purgatory (and sequel)