Let's play this game again

It hurts extremely because your whole body is physically altered.

Worth it.
There’s a whole fetish community that’s SOOOOO into this idea
RIP Scoot D:

You shift by magically turning yourself inside out ass first

Disgusting and likely painful, would have to be done somewhere private
- You're worried about manners??
  
  I mean, the point of shapeshifting is to be sneaky
  
  Something tells me you have less than honourable intentions for your newfound power
  
  I mean, what would you do with it? If I had it, I could greatly influence the politics of any country, simply by being any leader I wish to be and screwing their public image
  
  I would be a thespian of course! But now that you mention it, I can see the potential to use myself as a biological weapon to help bring about amore equitable world …
  
  TIL what thespian means. And I don’t think it would make you a better actor, just a cheaper and more versatile one. Besides, it’s funnier to kidnap random people and live their lives for a day. Since everything you need to know about them is inside a rectangle protected by the face and finger you just replicated, it should be feasible enough. Besides, they’ll take the experience to the grave or be considered nuts
From beneath you, it devours

Your brain shape shifts as well into an exact copy of the animal you mimic. You have the intelligence of the creature you turn into. Which means a one way trip as any coherent logical human thoughts is driven out by animal instincts.

If I shapeshift into another human, I’d just have their memories. Id have to shapeshift somewhere calm, and leave myself notes
- Oh my god, Memento meets Animorphs.
  Holy shit this is actually a good idea, I would actually read this book or watch this movie...
  It could also work in a video game, but it would be very difficult to pull this off as the player character... could make for some extremely interesting NPCs in various settings.
- This might make a good movie plot
  
  Give me the power, I’ll do it for free
- This would have infer that your shape shifting skill had the ability to mimic not just their DNA but their nueral patterns as well. Without that you are again just left with instinct and a blank slate brain with no memory or knowledge.

Your clothes are not transformed with you

Still works. I just gotta shapeshift into someone about my height
- You shapeshift, including your mind. When you change into a person, you take on all of their memories as well. You become a complete copy, and the old you simply ceases to exist. If you turn yourself into Donal Trump, there's just a random copy of the president sitting in your apartment, utterly confused about where he is or how he got there. And the ability to shapeshift was a power of your old body. The new one can't shapeshift.

But comes with body dysmorphic disorder. You’ll never be satisfied with how you look.

Not until you finally get it right, and at that point you look like a total freak to everyone else. But at least you're satisfied.

Your weight also change, but the difference is converted to energy using mass–energy equivalence formula.

Grow slowly -> walking air cooler
Shink rapidly -> Boom
- Wouldn't it be more like: Grow slowly -> burn proportional amount of calories Since you would need to get that energy from somewhere
  
  So you'd be interpolating between a keg-shaped dwarf and slenderman; sounds nice, too
  
  Honestly, I could probably get behind that lol. After long enough I bet you could get really good at getting your mass exactly how you wanted it depending on what you want to do.
So I just need to keep my weight constant

Granted, but you can never turn back

access to all animal shapes, but can only use them once, stuck in final form forever.
- Oh no... I'm a cat. Done and done.

You can only shapeshift into smaller versions of yourself.

That’s not really a side effect, more of a condition.
- Every time you shapeshift, you lose the ability to shape shift one more atom than the last time you shapeshifted?
  
  Like a Ramen card in Balatro

You forget what you like if you are changed for too long and don't have a detailed enough reference

A matter of keeping some hair in a jar as well as a photograph of mine
- Ide start an only fans account

You can only shift into a species that you've seen before. Can only shape shift into living things (not sentient and mobile inanimate objects)

And you can never return to any species you were previously. It has to be a new one every time until you exhaust the possible species. Leaving you stuck as the last possible species you pick to shape shift into.

Wait, but can I shapeshift within a given species?

you shapeshift, but your state and society will periodically and randomly remind you, that they know, what shape you had earlier ... wait, that does already exist. still superpower tho!

You can't actually become anything unique, the body approximately closest to your imagination becomes yours. They also, become you in turn. You immediately become a world wide sensation if used frequently.

That’s not shapeshifting, that’s body swapping
- fuck
  
  Still a cool power

Your telomeres become damaged every time you use the ability

You can also become invisible