Armor trims do not render on armor equipped on a Mime. This affects both vanilla and modded trim patterns/materials.
(The armor trim NBT data on the armor is copied over when a Mime copies a Player's equipment, it just does not render)

The outer layer of a Necromium Helmet does not render correctly when equipped on a Mime. The outer layer of the helmet's model is rendered slightly too low and rotates incorrectly when the Mime looks up or down, and during its walk animation.