Octopony (Poniworld Chronicles #7‪)‬

Mortimer is an octopony—half octopus, half pony—who laughs at all the wrong times. But he wasn’t laughing the day a gang of waterskiing squirrels kidnapped his girlfriend. He’s a joker, not a fighter, but it turns out the Nazi ponies have discovered an alien spacecraft buried in ice.
And so Morty ends up having to travel to the Arctic to foil a nefarious plot to unleash an alien supersoldier into Poniworld.
Along the way, he meets a mermaid he helps release from the clutches of a bearded clam. He also meets Santa Claus and teams up with the reindeer for a mission to infiltrate the Arctic stronghold.
It’s all very exciting and dangerous, and so sometimes Morty has these giggle fits, but it’s just because he’s nervous, so please don’t hold it against him.