Version Information

Minecraft: 1.12.2
Forge: 14.23.5.2806
Mantle: 1.12-1.3.3.39
Natura: 1.12.2-4.3.2.66

Imps have several small issues, most of them to do with breeding:

• Imps' hitboxes is too short as it doesn't cover their head, only their bodies
• Baby imps look exactly the same as adult ones, even though they have smaller hitboxes, as seen here
  
• Imps prioritise being tempted by their breeding items over breeding, unlike vanilla animals that stop being tempted as soon as they can breed to actually breed
• Imps (and other Natura entities) seem to have very jerky/laggy movement compared to other mobs