Mermaids.....?

They were in Sims 3, but not 1 or 2. They could grow legs and walk on land like normal Sims.

The Wiki has some good info on the matter.

Hmm.. interesting, but weird. I was hoping for some underwater action, but that’s ok too.

"Mindsimscreate;c-17085740" wrote:
Hmm.. interesting, but weird. I was hoping for some underwater action, but that’s ok too.

There is when they're in water. And the Isla Paradiso world in TS3 had scuba diving, so your mermaid sim could explore the sea without an oxygen tank. And sometimes you could meet mermaids too.

There were things to collect under the water including kelp, I think it was called. Sometimes, a shark came near you. I had one sim die that way. You can meet and talk to the mermaids & mermen. I enjoyed it tremendously and having a houseboat to take care of all needs and diving back in as soon as possible was great too.

There are a mermaid mod and custom trait

Mermaid Mod don't know if it's fixed yet or not.
http://modthesims.info/d/607804/mermaids-mod-v1-5-broken-read-description.html

Mermaid Trait
http://modthesims.info/d/606979/mermaid-quot-lifestate-quot.html

Mermaid Ears
http://modthesims.info/d/612078/mermaid-ears-swept-cas-preset.html

Mermaid Tail
https://www.thesimsresource.com/downloads/details/category/sims4-clothing-female-teenadultelder-swimwear/title/bottom-7-plus-invisible-feet/id/1426709/

https://www.thesimsresource.com/downloads/details/category/sims4-clothing-female-child-swimwear/title/bottom-10-plus-invisible-feet-and-nude-top/id/1445984/

https://www.thesimsresource.com/downloads/details/category/sims4-clothing-male-teenadultelder-swimwear/title/dsf-tail-triton/id/1446401/

In TS2 you could get them via CC. Someone, I forget who, made a CC item that provided a blue lower half and 2 seashells for a certain area on the upper half. It was available for all outfit categories except outerwear. There was also mermaid makeup, but not sure if by the same modder or different. Movement around the house had a swishing tail motion, and sims could do everything regular ones could. Made for some very interesting stories.

Someone is writing a story, in the story is a mermaid as one of the main characters in Sims 3. But basically, a TS3 mermaid would have legs while on land, but those legs would turn into a fishtail when they were well into the water (not including baths or showers).

https://forums.thesims.com/en_US/discussion/953861/the-cowboy-and-the-mermaid/p1