Alligator.

A large, black humanoid crocodile with a horn on its forehead emerged from the dark ball in the lake. when it was in the river bank It couldn't sense its fellow creatures coming from the same broodmother. It let out a loud roar that functioned like radar to locate nearby enemies. Upon spotting the enemies, it began moving towards them. 

Kay had a sense that something risky was approaching slowly. She decided to move towards the waterfall to get a better view of the lake below. It was there that she spotted the creature, which looked like a combination of a human and a crocodile. 

Lvl 10[----][Nightmare Alligator Man][Hp:10,000/10,000][ET:10,000/10,000]