Wild Squid

Wild Squids were level 37 mobs found around Nesaak and under the Nesaak Lake inside of the Squid Village. They were easy to kill and can't actually move unless in water. They were removed in the 1.14.1 update.

Tactics
You could easily camp them at the bottom of the lake. They gave out a decent amount of experience points when you're level 35-40, and were a mid-level mob to grind.