7. Forget The Tertiary Characters
Again, the whole Masters of the Universe world was originally based around action figures. You've gotta diversify the product so you can sell more product. Once the primary characters were in everyone's collection, Mattel took that same body mold that was used for 90% of the figures and spawned a barrage of supporting characters for the war in Eternia. The "Wave 1" characters all deserve a spot in the movie. He-Man, Man at Arms, Teela, Beast-Man, Mer-Man, Stratos...hell, even Zodac is fine. Even the "Wave 2" characters aren't too bad (e.g. Evil Lyn, Trap Jaw, Man-E-Faces, etc...). Once we start hitting "Wave 3", The character gallery hits a bit of a wall. The first two waves provide enough character variety for a trilogy of films. The following characters from waves 3-6 have no business being on screen (unless they are just momentary cannon fodder without a speaking part): Buzz-Off, Fisto (no jokes...), Mekaneck, Orko, Jitsu, Moss Man, Stinkor, Mantenna, Extendar (hey, still no jokes...), Snout Spout, Clamp Champ and Twistoid. A few of the later characters aren't bad for "goon" roles, and technically the Sorceress doesn't show up as a figure until wave 6, but we will be fine with the main stable for now.
The right decision: Show the formation of the core "Masters" a la Avengers or Fellowship of the Ring.
The wrong decision: Bringing in any of Hordak's crew.