Invalid Entity

This mod adds the Invalid Entity from Bionic's movie, Beyond The Border. Version and mod loader: 1.20.1 Forge. Watch the movie if you don't know or saw the entity. Mod ID: invalid.

Here is how it looks like:

It has white eyes with a black body.

This mod also adds the following blocks, items and biomes:

Invalid Spawn Egg (entity name: entity.minecraft.invalid)
Invalid Block
Invalid Biome (id: invalid_biome)
Invalid Fluid (in-game name: minecraft.item.invalid_fluid_bucket)

This mod also adds Steve to Minecraft as a neutral mob, meaning if you hit it once in survival, he will attack you.

To summon this entity, run /summon invalid:invalid. For Steve, type /summon invalid:steve.

This entity doesn't naturally spawn anywhere and has no AI. You can use a morph mod like Identity and Remorphed to morph into this entity and even troll your friends.

This entity is found when you break the World boundary using an NBT editor and going to X/Z ±30000900 and making sure the game still thinks X/Z ±30000000 as an invalid position.