The obvious one is Beowulf. A great lord's hall is regularly invaded by Grendel - an unstoppable water troll. The PCs must take Beowulf's place and defeat Grendel.
Then Grendel's mom comes for revenge.
See, that's just what I was thinking!
I drive a quantum car- every time I look down at the speedometer, I get lost.
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As a juggler, I may not always be smarter than a banana. However, bananas aren't often surrounded by children asking for hugs and autographs.