Operation guide: Mind the Doors

Other than the changed tileset, Mind the Doors is identical in all but name to Masterless Colossus. As such, the same strategy used in the said Ceobe's Fungimist Dreadful Foe also applies to this Phantom & Crimson Solitaire Dreadful Foe.

General strategies

Main article: Masterless Colossus/Guide

Therapist Medics can apply Status Resistance, so using them is recommended.
Surtr and Ch'en the Holungday are the best options to burst down the Lost Colossus with their Twilight and "Holiday Storm", respectively.
Lee's Preparedness Averts Peril will block the next Stun he receives and Stuns the source, making him the excellent option to bait the Colossus' boulder attack. Be sure to support Lee with at least one Vanguard due to the increased DP drain to trigger Preparedness Averts Peril.