Ring Selection - At the beginning of your turn, you may choose a Ring, remove it from the Power Plant and place it on a friendly character's card. That character can use that Ring's effects as if it were a relic. When that character clears, return any Rings on its character card onto the Power Plant

Can you choose more than one ring at the beginning of your turn if they are given to different characters?

Given the lack of use of plurals and words used to define multiples... I would wager the answer is 'No".

The use of "Rings" in the last part of the power leads me to believe one may have multiple ways of moving Rings around. (Does the Mandarin not grant such an ability?)

Anywho, I'm no expert, so feel free to disregard... this was just my $0.02 on the matter and an attempt at rules comprehension.

No. While the wording could be slightly better, I think it is pretty clear. "A ring" = 1 Ring. That's it, end of story.

That's what I thought but it never hurts to ask.

From the Player's Guide:

Unless otherwise noted, game effects only occur once each time they would apply. For example, "At the beginning of your turn, you may heal Wolverine of 1 damage" is an instruction to do this once.

I would think a character that has willpower and no tokens, at the beginning of your turn you place a ring on its card. Either perform an action with said character this turn our do nothing. Next turn, at the beginning, give the same character another ring, push with will power or give a first action. You only remove the rings when you clear that character of its tokens. So it is possible to give more than one ring.

Sure it's possible to have more than one ring out at a time, but that wasn't the question.

You could play Masters of Evil and never clear any of your characters, and every turn one ring makes it's way out to one of the characters until there are none left, but that isn't the same as assigning multiple characters a ring each during the same turn.

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As far as the OP goes, I agree with GeneralMalarky and The_Atom.

It says at the beginning of your turn you may choose a ring, blah, blah, blah.

If it was letting you give a character a free action to place a ring on their card then multiples would be allowed, but this wording seems very intentional in a way that doesn't allow that.