How to Stop Squids Spawning in Rivers but Keep Them in Oceans

Use biome conditions instead of a blanket ban

A global deny on squids would remove them everywhere, including oceans where you probably want them. Instead, write a rule that denies squids only in river biomes. In your config, set the mob/entity to the squid and add a biome condition listing the river biome(s). Leave oceans untouched so squids continue to spawn there naturally.

If the mod matches biomes by name, use the exact biome identifier the game uses. If you're unsure of the exact string, check an existing rule or the mod's documentation for the correct format rather than guessing.

Verify both biomes

After saving, reload the mod's rules with its command. Then visit a river and an ocean and observe squid behavior in each. Rivers should stop producing squids while oceans should keep producing them.

You can extend this pattern to other mobs and biomes — for example, denying a mob in one biome while allowing it in another. The key is always to scope the deny with a biome condition rather than banning the mob outright. If squids still appear in rivers, double-check the biome name and confirm no other rule is allowing them back in.