Here is a fun custom I did last year, this is Predacon, one of the aliens that was last introduced to GI Joe in about 1994 and left forgotten since.

Not specially my cup of tea, but I must admit it is a cool character, although more in Star Wars if you ask me! the vintage figure is quite forgettable, for my custom I based on the blister art, which is quite menacing.

Most complicated was engineering the arms articulations, so that all arms are fully poseable. I used a Venom body, which was curiously super articulated on arms, but nearly fixed legs, and combined it with a modern Thor.