Archived Kimimaru4000 video from YouTube. Original description mostly intact:

This video showcases the unused Koopa Curse item in Paper Mario: The Thousand Year Door.

Koopa Curse is a usable item in battle that inflicts the Slow status effect on a single enemy for three turns. The Slow status effect causes the character afflicted with it to move once every other turn. Slow is a very rare status effect since Beldam in the second Shadow Siren fight is the only enemy in the game who can inflict it on the player. Had Koopa Curse been included, it would have been a way for the player to inflict Slow on enemies.

More information about Koopa Curse as well as codes for adding it and other unused items to your inventory can be found here: https://tcrf.net/Paper_Mario:_The_Thousand-Year_Door/Unused_Items#Koopa_Curse

Thanks for watching!