Xaart
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I opened the map in the editor and carefully removed the magic clouds: there was no pit there originally. If it wasn't you who created it, then there's only one disappointing possibility: due to a bug in the game, some enemy hero flew there without having the right to do so (I've observed such flights repeatedly, and I have saves that demonstrate them).
The Grail was missing in the Necropolis of Jorune (cell 123.9) at the start. This means someone placed it there.
Jorune was a neutral Necropolis without a fort, defended by vampires and liches, and guarded by a guardian. When I arrived, there were heroes of green, but no one was taking the Necropolis. I was surprised to find the Grail there. Perhaps it's an AI cheat or a bug in the map itself. Oh well, I'll keep looking for a Berserker. If I don't find one, I'll start over.