Deeeep.io

In the game, you start as a fish, and eat XP sources to evolve into new animals. Several biomes exist in the game, including the Ocean, Reef, Kelp Forest, Arctic Ocean, Estuary, Swamp, and Lake. Each of these biomes has its own unique evolutions and XP sources. There is also a Deeeep Ocean, which spans underneath all the mentioned biomes. A variety of animals exist in the game, from sharks to birds, whales, and turtles.

Tier 1 animals (meaning the tier that the player spawns in as) don't drop XP upon death, and they cannot be killed directly by Tier 10 animals. Once a player reaches a Tier 8 evolution (meaning they have evolved 7 times), they are limited to picking a certain evolution after that. All players that are the same animal cannot hurt each other until they reach the Tier 10 evolution.