EDIT 2: It happened during scorpions' wave when Wickerbottom dropped staff near the edge, took petrifying tome, petrified all scorpions and Wolfgang used alternative hammer attack which pushed staff out of bounds.
Spoiler
Spoiler
Spoiler
Steps to Reproduce
Drop living staff near the edge, use alternative hammer attack in a radius of lying staff.
Drop living staff near the edge, use alternative hammer attack in a radius of lying staff.
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