When you spawn an iron golem, Minecraft may crash.
What I expect : The iron golem spawn normally.
What happened : The iron golem spawn and crash Minecraft.
When you try to reload the world, Minecraft crash again so you can't play world unless you use a 3 ^rd tool to delete the buggy iron golem
How to reproduce :
Spawn an iron golem as this
 P 
III
 I 
P = pumpkin
I = iron block