– Facing upward, 1 block above the pit floor. On top of the piston, place any block (this will be the "false floor").
You don’t need to kill the mob in all versions—just cause the “crush” event. But killing it is the surest way to pop the achievement.
: Equipping the hat on a character within the Ritual Background triggers the final unlock. Diversity of Achievements
Review: A Must-Have Guide for "Lovely Craft Piston Trap" Completionists