Forest Water. Used to heal the withering trees scattered around the Great Sea. An annoying side quest with a limited use item. Well, not anymore it seems. YouTube user Fish_waffle64 discovered that dumping some of the Forest Water on the exposed core of Kalle Demos will instantly kill it, greatly shortening the battle.
The weird thing about this is that people have tested it on the Gamecube version as well and it works. No idea why this little Easter egg hasn't jumped around the internet over the years, making this perhaps a newly discovered Easter egg.