Well, i think the idea isnt too bad.
But!!! There is somethin i would like to see different.
I would like to see, that it is only useable once! So maybe make it a potion instead? A single potion, that will instantly swap the two towers (Mirrage Rings). "potion of phaseshift" or whatever.
Even though, items are fine 2 things are so annoying that they probably wont be used:
Not beeing able to attack (if it counts for the whole min) and losing items. What if you lose lets say, Excalibur or even worse the Blood Demons Sword? I mean you forget the sword for whatever reason and the boom! wasted 397 lives for nothin...
Instant shift potion would at least be used ^^