This post will be a little more sci-fi than usual but, Masters of the Universe sort of bridges the gap between fantasy and sci-fi. For me, the creatures and monsters in fantasy-adventure films are really important and have been since Harryhausen.
The special make-up designs for Masters of the Universe were by Emmy and Oscar winner, Michael Westmore. Westmore is part of the famous make-up artist family of Westmores. He won his Oscar for 1985's Mask and was nominated for another for Star Trek: First Contact. He won several Emmys for his work on Star Trek: The Next Generation. Overall, I really like the look of the creatures in this film. The main problem with them is that most were done as full-face masks which gave the actors trouble with moving their mouths. As Westmore's technique developed, he fixed this problem for his Star Trek work.
Beast Man is a character from the original animated series so there was a clear guide for his design. This artwork is by production designer William Stout. It's pretty faithful to the original Beast Man design and Westmore's make-up is really successfully realized on actor Tony Carroll.
Saurod was a new character for Masters of the Universe but I think he fits really well into the rogues gallery. This design is by William Stout and the costume and make-up are really strongly realized on actor Pons Maar. You can barely see the tail in the film but it looks great!
Another new character for the film was the bounty hunter, Karg. Again, I like Westmore's design. It's very creepy and the costuming and hair coupled with Robert Towers' sort of androgynous performance make Karg really memorable. The problem with him was that his prosthetic was all one piece so his mouth doesn't move believably.
The character of Orko was too complex to create on film in 1987 so he was replaced with another new character, Gwildor. Gwildor was played by the famous Billy Barty and he does a good job getting his performance through a really complicated make-up. Again, Gwildor looks great in still frame but his mouth doesn't really move when he talks.
Finally, you couldn't make this movie without a great Skeletor. I like the casting of Frank Langella even though he's totally unrecognizable. Westmore's make-up is really good but I think I would have preferred to have black around his eyes. No doubt the filmmakers thought that would deaden his performance too much.
A great source for more information and artwork about this film is He-Man.org.