It should cost an Iridescent Gem instead of a Purple Gem.
After using the Celestial Portal, it will go on a 20 day cooldown for the person who used it.
The point of the Celestial Portal is to give an option to change a character for people who got bored of the character they were playing.
Implementing the cooldown and the cost would make it actually fulfill this purpose, instead of being a machine to use other characters’ perks for a moment and then switch back.