I deleted the mascot's tombstone, no change.
If you deleted his tombstone, then his ghost shouldn't be appearing anymore, should it?
It sounds like the ghost has taken up residence in that floor tile somehow .....
I'd be tempted to deleted the ghost's character file, but from what I've been reading here on the forum that could be problematic if you don't delete everyone's memories of him as well.
Curiouser and curiouser ......
Edited to add: I was just looking at the thread on being scared by a lamp (http://www.moreawesomethanyou.com/smf/index.php?topic=89.0), and it made me wonder if you'd tried the updated lot debugger?