Obviously I'm on the PC, and know a little about using the console. I remember reading, years ago, how to fix the glitch where an NPC has 2 heads, one that animates and one 'on top' that does not. This has happened to a few NPC's in the past but they were just guards and stuff. It has now happened to Martin in my current game, so I kinda need to get it fixed. Help?

Double-face bug happens when you fast travel with a follower. UOP provides an "on touch" spell to cure it, and adds it to your list.

IIRC you can do the same thing with either kill/resurrect commands or disable/enable via console, but there may be side-effects of doing those with some characters. E.g. if you kill Martin the game ends before you can resurrect him.

It may also go away if you leave the cell they're in and re-enter, which is only useful if you can go outside/inside without them following.

The simplest way I've found of dealing with that fast-travel double-face bug is to save right after fast-traveling, quit to the main menu, and reload the save.