There's a known bug in this room because the challenge was grafted on to an existing script
If the tar mother spawns on a
previous visit to the room, the script will End and you'll never get the challenge on subsequent visits. One of the classic blunders we tell architects to watch out for these days.
To get round this, use Restore ->
Room Start to get a "
clean slate"
version of the room. If you step on a checkpoint (in another room) before restoring, you can subsequently restore to that checkpoint to regain your progress.
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50th Skywatcher