Depends on the version. You can look for Baleful Polymorph or Reincarnation spells. Possibly Wish. But the best solution is to talk to the GM and let them know what you want. They can come up with a solution that works in their setting.

Is 5e and thank you will look into those as well as have a chat with the DM ahead of time, he knows about the character trait im hoping to do but we haven't gone into detail about it yet (gave him a big smile thoe lol)

Wish, miracle, curses, polymorph spells. Any item that duplicates those effect. Some are cursed items (can't be removed except through magic). If a god, demon or other supernatural creature did it, it's gonna be permanent unless another similiar being reverses it.

I see now that last part is quite interesting as that could be exactly what i need to make it work thank you :3 The main thing thoe is I just want a way for the ferret anthro to be in the world as a player but keeping within the rule set, other than occasional confusion to new people (up to DM of course) its not ment to be a driving force behind his character just a trait in the same way someone may have a unmissable scar that covers a large part of there body :3

Could always say it was a botched Polymorph spell from the trick, and a Permanency spell got used.

Interesting :3 again can look into this ty ^.^ Im trying not to make the backstory to complex just like said above i wanna keep within the rule set (current backstory in short is a human thief (no one special just a bit egotistic) kept claiming he was the best around an he could outwit anyone, well he dident lol and upon trying to outwit a powerful being he was transformed into a ferret :3 a fitting form for such a sneaky thief (again intended as a punishment or trick but Kiba will grow to like it :3 so he gets the last laugh i guess x3)

there is a variety of things that could cause that. many of which have already been mentioned by others above. But the beauty of D&D is that you aren't really constrained by the rules, it even says in the players handguide for 5e that if a rule doesnt work for your group, feel free to try something different. most DM's will use homebrew content. either stuff others have made, or stuff the DM has made themselves. keeps the game interesting and makes each group different.

so my advice is talk to your DM, work out something that fits both your characters backstory and the campaign setting, and think of story hooks the DM can use to expand on this as the game progresses (the DM can do this on their own, but it makes their job easier).

Thank You~ an that is true just i got worried about being one of "those" players who makes a wild an complicated backstory something that really dosent sync well with the world/campaign . Our DM is super friendly an paitaint but at same time i just wanna have this ready for when we start this weekend so im not spending the first few hours trying to fine tune the character before we can even start ^^;

I agree with this comment (really, the most complex part about this character is coming up with stats for their anthro Ferret form, and that's pretty easy).

People are kinda touching upon both sides here.

Mechanically it is possible to have yourself turn into an animal, but on the flip side, maybe your DM would allow you to just be one. Like maybe your animal is a race in this world.

But another important thing to consider are the people you're playing with. If theyre other furries, great! No problem. Otherwise, ask your DM and even the players if theyre okay with it.

Ty an thats true just ideally id like this to be a transformation :3 as for the others there all fine with it ^.^ one is a furry anyways, like said thoe as this is the first full on serious thing now (e.g before now ive made characters on the fly for short fun sessions) i want to do things properly ;3 the others are more experienced so im already gunna be full of axienty not wanting to frustrate them ^^; but i also wanna bring my own personality into this an be a character they enjoy having around :3

Oh good. Then I'd say no problem on that front!

If theyre good players, theey should even help you. Everyone has gaps in DnD knowledge afterall.

My advice then. Make sure you know what you want to play, and furthermore, how to achive that mechanically. What class to take, skills to prioritize, gear to buy. Run the idea through your head, if you can even make your character and playtest him. Even better!

Yus an no worries ive got that covered ^^ theres a reason hes called Kiba Traptail x3 (he would have you believe its due to being good with traps, the true story is alot more embarrassing XD)

A story Im sure the PCs would love to hear ^^

Hope so x3

the easiest way to have him perma ferreted is to have in his backstory that he managed to wander into the faewild and accidentally insult an archfey who curses him

Maybe thoe as hes a common thief would that be something he would do i wander :3 (as in would his wanderings take him that way)

maybe he was running from the law and hiding in a forest when he got lost in the faewild? stealing an artifact from an archfey would guarantee a cursing.

The beautiful thing with D&D is that your options are only really limited by the creativity between you and your DM. As others above have said, Wish and True Polymorph would be the spells I'd jump to keep it by the book. However curses or gifts from gods, demons or other entities could accomplish the same thing in addition to cursed/magical items [stealing a magical item that makes the user more stealthy instead of paying for it could have a "punishment" ;) ]. Few things in D&D are truly permanent (though a lot more are functionally permanent dependent on player level/desire). So overall, be creative with your DM so it fits into their setting for the game. :D

To give two brief examples from my experiences:
- My last character, a ranger named Stekvidd, fled his home but in the woods turned into an anthro wolf (in setting known as wolfen) over about 6 months, but the reasons to why were uncertain (I left that to my DM as I wanted to roleplay him learning). Fast forward about 20 sessions and he goes on a one session sidequest, ends up in the Feywild and meets an entity only revealing himself as "The Wolf". The Wolf, as we found out, had chosen Stekvidd to be his champion in order to slay a white dragon. His transformation was due to The Wolf's "gift", which by that point Stekvidd had already accepted who he was now.
- I'm actually jumping into the DM role in the near future for a pirate campaign. Working with one of my players who will start out human, but through a cursed flintlock, will slowly turn into a sharkfolk. The transformation progresses with his horrible 'monstrous' deeds (at the moment to save his kidnapped family but subject to change, going for a fall from grace kind of arc).

In the end, you have so many options available you can craft something that fits your desire for your character's background, personality and motivation and make it work in setting. :D
*noms cookie*

I'd say probably the best spell to be cursed with is True Polymorph, a very powerful spell at 9th level and can cause a permanent transformation. On how to make an anthro ferret work as a race I'd suggest maybe trying a reskinned Tabaxi where you're a ferret instead of a cat. Then you'll get neat features like claws and a free burst of speed. Of course all of this depends on what your DM will or will not allow. Work with them to figure out how to get your character to work. Have fun!

if you wanted to progress into it i think the wildhunt shifter as the race would be a fair start. you could work in how the encounter with whom ever makes you a full blown ferret. :3

Honestly depends on how you want it. A lot of DM's are cool with something you want just replicating another race's mechanics for the sake of gameplay. There are also a lot of options to get what you want like with Shifters from Eberron, explaining your backstory via a curse (and curses can be permanent if Ravenloft has anything to say about it), or there's -some- homebrew content that's out there which is absolutely fun to play.

Merceau is a reskinned tabaxi for all intents and purposes (instead of a claw attack he can bite) - I've repurposed him using homebrew nezumi rules, ratfolk rules, and even a DM's take on their own custom race. No matter how you wanna swing it you should be able to do what you want.

Just be prepared if not everyone is ready to see an awesome ferretman. ;)

Cool a permanent curse tf into a bear

Easily can just say ya got cursed by a true Polymorph spell/curse from a person/object, can even change gender if be. It really wouldn’t matter in the case due to, heck it’s dnd. You can really make up anything and have it be right so long it fits with the setting of the world the DM makes.

Assuming you're talking 5e here, strictly out of the books true polymorph, wish, and divine intervention come to mind. All of these would be "permanent" in the sense that they wouldn't just wear off on their own (it would actually take essentially the same methods to undo it). But as this is less than official, can probably just talk to your DM to make it a part of your story in some way. Each would make sense if someone was trying to "curse" you or even give you what they thought you wanted, and could make an interesting story as to how your character got that way.

Mechanically I'd ask the DM to essentially let you play a re-flavored tabaxi, as their abilities are pretty similar to an anthro creature with high dexterity and abilities that make them quite fast. And their stats make for good rogues already.

I think thematically a "curse" (or possibly even a blessing, from their point of view) from a Trickery domain deity or cleric of such would work really well in accomplishing what you're after, in a way that fits the D&D setting quite well. (Or making a wish to a mischievous wish granting entity, like a genie or efreeti.) It's probably what most people in universe would assume likely happened to you, in a world where magic is known to exist and animal people are quite rare (they're known to exist but are a very small percentage of the humanoid population).

Honestly just talk to your DM. D&D's lore is meant to fit various types of fantasy so you shouldn't really worry about the nitty gritty of it. Things can be added to make your character idea work.

There are many different effects that could qualify, a permanent polymorph spell being a likely candidate, wish, an encounter with a being that can change reality. Could be a primal curse that is immune to dispell magic or the "blessing" of a higher being. To be honest, the sky is the limit as long as you can run it by your dm. You could possibly have this reflected in race and retheme a Shifter (if 4e or 5e) to be ferret based, shifting being when you let the curse or spell affect you just a bit more. Or retheme a tabaxi for the rougish anthro. Though all that should be ran by your dm before it's made into your lore, as it still has to work in the world he created.

There is a spell called permanency that does what the name implies. You can always use that!

If you chose to go with infected lycanthropy, then a true were-ferret might have scratched or bitten your human rogue and then you would spend your spare time looking for the cure.

Also, remember this one extra rule... it isn't a curse if you are enjoying it.

My two cents from a former dungeon master turned writer.

Most gms, including myself, would easily allow that as part of a character, racially they are functionally a human but cursed to look like something else, even as a custom race, while not advised as most gms will deny a custom race on principle, that is just a reskinned human you can usually talk a gm into it. Aside from that there are only homebrew spells or normal polymorph playing with its permancy point system to accomplish what you want.

If this were D&D 3.5, and your DM allowed you to make use of the anthropomorphic animal template in the Savage Species supplement, I'd say use that. Otherwise, it's definitely something to discuss with the DM and the other players. Especially the DM, as they may have further limitations on what you can do in the setting.

At the end of the day though, it's best not to get too hung up on game mechanics if roleplay is what you're after. That doesn't mean you shouldn't try to build your character to suit the roleplay, but game mechanics don't cover cosmetics or general behaviour in D&D, both of which being handled through roleplay alone, and curses of this sort are no different. At best, it provides a plot hook for an adventure arc in the campaign you're taking part in.

there doesn't always have to be something already existing in-universe to perfectly fit a reason for it, as long as your DM is open to the idea and willing to work out some reason for it there shouldn't be a reason why not

The fun thing about Dungeons and Dragons is that magic doesn’t always have to have specific rules, particularly if it’s really weird. I’ve seen Dungeon Masters turn characters into clockwork constructs with very little rules pretext, countless other weird shit too. Your idea may not exactly conform to the rules, but your Dungeon Master can make it work.

UPDATE - Thank you for all the help everyone i have read every comment an opinion im just sorry ive not had time to answer them all, I will however be doing an update journal shortly (good an bad news)