Early in Series 5, the Corridor of Blades was still a relatively new obstacle. It would have undermined it to introduce the idea of a spell being necessary (or even merely helpful) to survive it. As a watcher, I'd have been unimpressed to see a dungeoneer standing in this tense and deadly location, totally impervious to blade after blade, because of a spell they'd got off a scroll. The idea of a Corridor of Blades survival spell was only introduced in the last quest of Series 8 (BURST). Even then, it was because Lord Fear had made the blades faster than normal. The GHOST spell in Series 3, which turned dungeoneer Martin into a ghost, was highly unusual in getting the team past more than one obstacle: a wall and a wellway guard. There's no evidence that GHOST in Series 5 would have been similar. It may, for example, have summoned a haunting. Or it could have neutralised an adversary by making them faded. (After all, SPEED in Series 3 affected the dungeoneer while the same-named spell in Series 8 affected the room.)