So I spent a bit of time refreshing myself on Korean mythical creatures. Most are pretty much the same as Chinese/Japanese ones, just with different names.
One that came up today (I went looking for it, actually, and learned something new) is the Bulgasari (also spelled Pulgasari depending on your Romanization system).
Now, in modern Korean, bulgasari 불가사리 means starfish. Just the aquatic animal.
But there was also a North Korean giant monster movie commissioned by Kim Jong-il in 1985 called Pulgasari (same spelling in Hangeul as the starfish). I was thinking I'd read up on the NorKo kaiju to include it in my game.
But then I discovered there is a mythical creature called the bulgasari 불가살이. Same pronunciation, but different spelling (and different Chinese characters if you look them up). This one means undying beast.
I found this wonderful little blog that stopped updating after only a few months. It tells of the mythical creature. It looks like the baku or shirokinukatsukami -- a bear's body covered in scales, an elephant-like head, a cow's tail, and tiger paws. It was immortal and ate metal.
Well, immortal is no fun for D&D, but eating metal? Guess how I'm reskinning the rust monster for TSR-East!