Spawn

Marco morphed as Spawn, hiding under David's bed.

"I just wish my snake had been out of his box. He's had his venom taken out, but I bet it would have scared those birds."
"Snake?"
"Yeah, he's really cool. He's a cobra. You're not even supposed to be able to own them, but my dad got it for me."

―David and Marco

Spawn was David's pet king cobra who slept under David's bed. Despite cobras not being allowed as household pets, David's father had gotten his son the snake, although Spawn was defanged. Marco acquired and morphed him in The Discovery, although Spawn was mistaken for Marco in morph and taken away by the Yeerks, and subsequently killed.

History

"But what they saw on the floor was not me. It was Spawn. The Hork-Bajir threw a towel over Spawn and gathered him up. They stomped away, down the stairs, carrying what they thought was an Andalite in morph. I didn't want to think what they'd do to the poor snake. Maybe just hold him, waiting for him to demorph. But maybe when they realized that wasn't happening, they'd do other things. Visser Three is an evil, vengeful creature."

―Marco

Spawn is first mentioned by David when he tells Marco that he wishes Spawn was out of his box to scare off the osprey and the bald eagle that broke into his room. The next day, Marco hides under the bed and acquires Spawn, and then morphs him as it is the only animal that could be in David's room and not be suspicious. Unable to stop David's email to the Yeerks from being sent, Marco is forced to remain in cobra morph as the Yeerks arrive. When Visser Three and several Hork-Bajir storm David's house, a massive fight ensues. The Yeerks realize that one of the "Andalite bandits" are in a snake morph, but they take the real Spawn, not Marco. A Hork-Bajir wraps him up in a towel and carries him down the stairs, with Marco musing that Visser Three would torture the snake thinking he was an Andalite, and then destroy him when he realized it wasn't going to demorph.