This works for the mermaid tail, too bad it’s expired
First make a new account.
You must go to Early Poptropica and don’t go in any rooms/maps
(Credit to KeithSammut for old ad glitch)
Now launch avatar studio AFTER you’ve arrived on the island.
Then type in TESSMARIAHGIO14 and refresh the page.
I do have a screenshot.
However, once you go to another relatively newer island, no more mermaid tail.
Sorta sad, it was a great costume piece.
P.S This is mainly for Perfect Coyote to prove something but also grants a few less rare things.