Heman and She-Ra... the thing that bothered me the most about them, was the fact that they looked almost exactly like their original forms after transformation... only more slutty :).
As the transformation was all about the "power", I thought about giving them invincible energy forms, instead of a loincloth. I also tied them to Skeletor's back story, as he was mangled while trying to harness this power for himself. I also tried to address the question of "why were Adam and Adora chosen?"

Skeletor! I gave him a more elaborate armor (as in "less naked") and, hopefully, made him more menacing (as if a yellow skull for a face was not enough). Seriously, I loved his design and didn't change that much. His chest piece was made to reflect his position as the king of Snake mountain though.

Hordak was chalk white, with red teeth and a skull bat for an emblem... how was he not a vampire?!?
I always liked it when he turned his arms to flamethrowers or laser cannons, And he could change his entire form - one time he turned into a rocket! So cool!
So I just took it a few steps forward, with blades and monster parts... seemed reasonable.

Although her voice was, often, annoying, I loved her panther transformation! I thought it would be cooler if it was not a magical tiara who did that, but some shamanistic, primal, force. So the tiara became a Smilodon's skull with a dark animal spirit bound to it. The Grizzlor image is from a redesign of him I was not content with but felt it fit perfectly in this capacity.

So why would a regular looking woman (by Heman universe standards), would have tiny scorpion claws and tail and nothing more? Were those glued on? Could she take them off? What if she was forced to wear them? How would life be like if you had to be a scorpion, but didn't want to... Those were my thoughts as I designed Scorpia and her new backstory...

Mantenna was was always weird and kind of goofy... I did love that his eyes popped out on stalks, it made me think "insectoid/crustacean" and the weirdest of those was the mantis shrimp (- who can see colors humans cannot, by the way!), so I gave him Mantis Shrimp eyes and just envisioned him being able to see into other dimensions, radiating different energies from his eyes, scuttling about and making people feel uncomfortable...

I've never seen Modulok in action, but his toy looked awesome and I read about him. He WAS a scientist that had an accident that changed him, I just connected it to the Hordak concept of "being able to change at will", to make him belong with the Horde and have someone who would invent new menaces for the heroes!

With so many spider qualities AND the word "Web" in his name, it was surprising how few limbs he actually had! As an infiltrator and spy, his large metal grappling hook and big noisy gun, seemed a bit excessive... The web shooting is obviously borrowed from Spiderman, and the idea to fashion weapons from the web fluid came from a Naruto villain called Kidōmaru (although he would "puke" the material).

We never learn if Mosquitor is a human with a mask, half machine, a mutant, or all of the above... I tried to sustain the mystery by giving him suit of power armor, and a retracting (again, just imagine him trying to navigate a room with that spike extruding from his face... ) stinger that can inject poison, blow gas, spray acid and maybe even shoot the barb. The stinger is hooked to a pump on his back, that stores dangerous materials he can use to make the poisons even mid battle.

Imp was always this annoying kid that never bullied you directly, but was always there, sneering at you from behind the actual bully's back... that's how I envisioned Imp... that and "what if Chucky the murder doll could change shape at will"...

Spikor always looked menacing, like he could do some damage and his trident hand made me think of gladiators, so he became an ex gladiator champion. I gave him an extended claw arm because it made sense for his fight style to utilize his spikes as much as possible... imagine how dramatic a "Teela being pulled towards the spikes, only to be saved in the last moment" could be... Also, I got rid of his black speedos... they had to go!

I read somewhere that he could "dissattach" (that is NOT a word!) himself and reattach back, although I never saw it happening in the show. I imagined how their fighting style would change, from wielding a huge two handed sword and being able to only use the metal cable (as two smaller beings), to attacking quickly with that huge sword and flailing that big spiky ball around with synchronization and ease (when bonded).

So what if leeches evolved to a point they could speak and walk upright AND be bigger than humans... Is a question not enough people ask themselves... but I did!
Leeches and Lampreys are alien as is, but I also imagined him as a lumbering giant, always hungry, that almost nothing phases... slow but unstoppable. I also wanted him to be able to talk, so I envisioned an inner mouth just for that.

The scrawny neck that can magically extend looked a bit strange, so I made it fold in on itself, like a turtle neck... only faster.

The original Tunglashor was in great shape! (to fit his toy mold probably), but I wanted him to swallow his enemies whole! So I gave him a, slightly, more intimidating tongue and the constitution to do just that! (It maybe hard to see, but there's a "digesting Tunglashor" pencil sketch at the bottom right. Also, why would a snake wear panties?... No.

It was strange to try and imagine Squeeze just walking about... not to mention running, without tripping over his arms! So, not unlike Rattlor's neck, his arms can retract, not like a turtle neck this time, but more like a very fast snail stalk. The longer he extends it, the thinner it becomes, until it's translucent.

I gave him hollow fangs with the hole facing forward, like a spitting cobra. Got rid of his suspenders and (admittedly cool) scaly panties...

So there were a lot of snake villains in the show. They were all part of the same group called "Snake Men", Simply horrifying! I made them all experiments of Modular that he lost control over and became, eventually, an independent group of baddies.
King Hiss looked cool! But I thought a huge, hydra like creatures, might be even better... eventually I went with the concept of a "Rat King" but with snakes (check the freaky phenomena here - https://en.wikipedia.org/wiki/Rat_king).