Version note: Open Beta guide; do not assume retail achievement behavior survives unchanged.
Where you meet Tar Golem
Prologue — first major fight, route gate before Marrow Keep
Role
The Open Beta's first main boss and the prologue's route transition.
Approach
Learn Harden timing before rushing. Two phases; watch the danger tells and punish in verified safe windows after heavy swings. Keep a ranged sidearm ready.
Missable check
Missable: A zero-health achievement is tied to this fight: defeat Tar Golem on the first attempt before its defeat cutscene completes. If you've passed that sequence, a new save is the cited retry route.
Source
GamesRadar: How to get the Mortal Shell 2 Tar Golem achievement