[Exit]
This is the junction between the intermediary layer and Old Derry Town.
Pennywise, and the recently killed "Mutant Doctor", must have entered the intermediary layer from [Exit].
And in the end, only Pennywise managed to break free from the constraints of Old Derry Town and escape to New Derry Town, thus starting his new life.
Subsequently.
As the World of Fate constantly improved, [Exit] became reinforced and no inverted entries were allowed.
Because of this, Pennywise was able to confidently build his 'PlayTown' in New Derry Town.
When he heard that they were going to 'repair [Exit]'.
Pennywise, all the way, even when encountering the "Mutant Doctor", always kept a playful and jovial attitude, but for the first time, he revealed an uneasy look.
"[Exit] can never be destroyed ... never! There is no [Exit] in Old Derry Town. Unless..."
"Unless it's destroyed from within the intermediary layer." Han Dong added.