If you want your mermaid Sim to become a regular Sim, you can do it with a little help from Mermaid Kelp. Eat two pieces of it, then swim in any body of water, and the transformation happens. Both pieces of Mermaid Kelp need to be eaten within four hours of each other.
Once you swim a bit, the transformation is complete, and your mermaid becomes a normal Sim.
You can always switch back. Eating another two pieces of Mermaid Kelp and taking a quick ocean swim restores the mermaid form.
How to Get Mermaid Kelp
The fastest way to get Mermaid Kelp is to spend 500 Satisfaction Points in the Rewards Store. If you prefer exploring, diving for lost treasures in the ocean can yield Mermaid Kelp, too.
Certain hidden locations, like caves on Mua Pel’Am, are also good spots to find it.
Keep in mind that after eating the kelp, you have 24 hours to swim and complete the transformation and become a mermaid. If you wait too long, the effect fades, and you’ll need to start over.
Cheat Option
If you want to skip the Mermaid Kelp route, cheats let you turn your mermaid back into a normal Sim instantly. First, open the Cheats Console by pressing Ctrl + Shift + C at the same time.
Once the console is open, type testingcheats true to enable cheats.
Then enter: traits.remove_trait trait_OccultMermaid
Your mermaid will become a normal Sim. You won’t get a notification, but you can check that their Hydration need is gone and replaced by the regular Hygiene need.
You can also go the other way. If you want a normal Sim to become a mermaid, use this cheat: traits.equip_trait trait_OccultMermaid.
Happy Simming!