"Dark form" for normal Sims?

I've made a vampire look like an alien before. Sunlight- just read vampire tomes until you gain enough points to become immune to sunlight. Do it consistently and it should only last a few simlish days.

Werewolves on a vampire base can be amazing, if you're willing to use some mods. Little Miss Sam has one called New Vampire powers that makes your werewolf immune to sunlight, able to eat human food and gives them a mirror reflection. Then there's an Eat raw fish mod at MTS that can take care of feeding if your werewolf doesn't want to eat cooked dishes.

From vanilla game Uncontrolled Hissing and Improved Athletics are good werewolf perks/quirks to have.

(About the original question, I unfortunately know nothing about such a cheat/mod, but would be interested in one!)

No, there isn't, but as mentioned prior, a werewolf made from a vampire has everything you'd need (including the aesthetic details), and if it's ranking and points that are holding you back, you can study vampires on the computer or read the ultimate tome indefinitely. As for thirst, you can still eat if you don't take Withered Stomach, and simply subsist off of packs (or download LMS' mod, as mentioned). As for vampire interactions...just don't use them.

Okie dokie, then! Many thanks ?

I would love for the poor Aliens to actually get the copy to guise just like the Vampires have for dark form.
Also, the poor Mermaids needs a better copy to for their tails.