viewtopic.php?f=9&t=1657
Global: Pay [Mask]. Move up to 2 Sidekick dice from your Used Pile to your Prep Area.
If during my opponent's turn, there are 3 Sidekick dice in my Used Pile, can I use Professor X's ability twice? If yes, and I pay using Sidekick dice each time, will it let me move 4 Sidekick dice or only 3?
ANSWER: Yes, and 4. You perform as much of Professor X's card text as possible after paying all costs. The first instance of the ability would resolve completely, at the end of which the Sidekick die you used to pay its cost moves to your Used Pile (it is your opponent's turn). Even though you've already declared that you are using the second instance of Professor X's ability, it now resolves when there are 2 Sidekicks you may move to your Prep Area.
I am sure it was just overlooked during the time when the rule was changed. Just don't want future players to get confused.