Hmm...there probably aren't a lot of animals that are a downgrade from my wretched human body.
Maybe a sloth? The power of...slowness...yeah, not very appealing.
On the same line of thought, a snail would also be pretty disappointing. Especially if I'm a Den Den Mushi. People trying to use me to make calls all day? No thank you.
Maybe a platypus? They don't do much, after all.
A naked mole rat. Though, I do have a taste for Nacos.
A fly? Throwing up on my food doesn't sound like much fun.
A skunk. We've seen before that no one loves a skunk. And you WILL get cancelled.
A tapeworm. The power to be a stomach parasite. Effective? Maybe. Gross? Definitely.
A dung beetle. Life's already hard enough, man.
Most sea animals. But, I'll say specifically a sea cucumber. You can't swim. I guess you might still be able to breathe underwater? But, if it saps all your strength, you wouldn't be able to move anyway. The power to throw your own intestines up at people? It's a unique power, but not very appealing.