Put the summary of the bug you're having here

What I expected to happen was...:
The world would lag a bit, of course. I just wanted to see the new creature in "person"

What actually happened was...:
Spawning more than 20 Guardians, all within a distance of 20 blocks of each other crashes the game.

Steps to Reproduce:
1. Spawning between 5 and 10 of these reduces the fps to under 10.
2.Spawning between 15 and 20 lowers it below 5 fps.
(So even if you have stopped clicking, they will still spawn.)
3. Spawning over 20 crashes Minecraft completely.