Here are two creatures that actually exist, but shouldn't. They also explain why our ancestors got the hell out of the ocean millions of years ago.
1. Blobfish (Psychrolutes marcidus)
The blobfish may be facing extinction, and that's probably a good thing. They're so ugly they're cute, and back to ugly again.
2. Goblin Shark (Mitsukurina owstoni)
"Goblin Shark" is but a rough translation of the original Japanese name, which can only be pronounced properly while projectile vomiting. The very existence of such an animal should make you pray for death. Of course, this prayer would go unanswered, because any universe that would include a Goblin Shark is surely devoid of any deity, let alone a merciful one.
Both the Blobfish and Goblin Shark live in the deep ocean where sunlight doesn't reach. It's a common misconception that sunlight isn't capable of penetrating the ocean depths, but the truth is that it chooses not to. Because it is scared shitless.