The Guardian is a mob with laser-shooting abilities. They spawn in Ocean Monuments, and protect the Elder Guardians in the monument. These spikey fish are not to be underestimated. One Guardian is simple to take care of, but a herd of them and you're in trouble!

More info on Guardians: https://minecraft.fandom.com/wiki/Guardian

Credits: I got the textures for the Guardian at https://www.tynker.com/, which is a coding website for kids, including Minecraft coding.