If you couldn't kill the orc drummer on level 50, that sounds like a bug.
The Shrimpo quest is gotten as you leave the graveyard after getting out of Iona's dungeon. It can be solved in the graveyard.
In the north east part of the graveyard there are a set of gravestones in a rough circle...[spoiler]read in the correct order, the first letter of the names on each tombstone spell out S H R I M P O.
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