It's all in the cards!
Henzell says...
Derived undead and various Crypt undead slowly replace each gravestone over time spent on in the wizlab. Once most are slain, a door appears at the start where liches and an ancient champion guard the twin tombstones of the house of Zonguldrok, which both spawn {antique champion}s when you walk past them to get to the loot.

Information based on master branch and the great LearnDB.
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