The ocean is one of the largest biomes, covering around 60% of the Overworld. The warm ocean is a variant of this biome. As the name implies, warm oceans will have water that is warmer than its other variants like frozen water, lukewarm ocean and cold ocean.
The warm ocean biome has a green tone to its water. It is the only ocean biome which has coral reefs. These coral reefs are found in the form of coral blocks. Additionally, this biome is also populated with seagrass, kelp and sea pickles. This biome also has its deeper variant which is called Deep Warm Ocean. This rarer biome has twice the depth of the warm ocean biome. Deep oceans are the places where ocean monuments will spawn, making them the natural habitat of guardians and elder guardians.
The mobs found here are guardians, elder guardians, squid, fish, dolphins and turtles. Hostile mobs won't spawn in the water but the drowned can pose a threat to unsuspecting players.
Oceans are possibly one of the most inhospitable places in the Overworld for players. Masked by the lack of most mobs is the risk of drowning. A player can easily drown while attempting to dive deep underwater without protection. This biome offers isolation if that is what one is looking for.
A. Warm, lukewarm and frozen oceans are considered extremely rare.
A. Yes, there is a deep ocean variant where the depth is twice that of a normal ocean.
A. Yes- guardians, elder guardians, squid, fish, dolphins and turtles can spawn here.