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
Version Information
Minecraft:1.12.2Forge:14.23.5.2806Mantle:1.12-1.3.3.39Natura:1.12.2-4.3.2.66Imps have several small issues, most of them to do with breeding: