This came up today -- our Argent Adept player played Arcane Cadence (his one play for the turn while the Impusion Beam was out), and then wondered: what became of the 5th card that it directs him to play? (Note that the card is to be played, not placed into play).
Option 1: It gets trashed because it can't get played. This was my first thought, but I couldn't find any support in rules or errata.
Option 2: It remains revealed but is never placed or replaced anywhere, lost forever in space time until La Capitan rescues it. This seems to be such a counterintuitive and counterproductive option that it should be rejected.
Option 3: Because "nothing happens," it goes back where it came from: on top of AA's deck. This is what we ended up doing, because the resulting state of the game best reflects the prevented effect never having occurred at all.
For reference:
Arcane Cadence: Reveal the top 5 cards of your deck. Put one into your hand, one on top of the deck, one on the bottom of the deck, one into the trash, and play one.
Impulsion Beam: Each player cannot play more than 1 hero card per turn. Each hero cannot use more than 1 power per turn.
Arcane Cadence puts a card into play. That is different than a player playing a card, which is what Impulsion Beam prevents. There is a difference between a card being "put into play" and "playing" a card in SotM.
For instance, Omnitron-X can play a card in his play phase but still use his power to put the top card of his deck into play.
Thanks for the response -- I assumed that would be the case too, but I was tripped up by Arcane Cadence explicitly stating "play" and not "put into play." The relevant section in the Spiffrata collection seemed to reinforce this.
“Playing” cards vs. “putting cards into play”
“Playing a card” means putting a card from the top of a deck or a hand into play. “Putting a card into play” is a different action than this. This means that effects that prevent cards from being played do not also prevent bringing cards into play in other ways (for example, by an effect which brought a card back from the trash into play).
Don't trust Foote, I think he's wrong in this instance.
I have no concrete idea what would happen to the card and I'm pretty sure you can't play it (because it is play and not put into play as you rightly point out) but I would hazzard a guess that it is discarded without effect.
I remember someone pointing out the difference between "play" vs "put into play" due to Matriarch's ability and Darken the Sky. She can't play the top card of her deck if a fowl is put INTO play, but she can do so if it was PLAYED.
So I think Arcane Cadence does not allow you to play the fifth card.
The definition of playing a hero card is "Hero cards are played from players' hands" (per the rulebook). Since the card that Arcane Cadence is playing doesn't come from your hand, I'd say it gets played. Just like how Omnitron can put cards into play from his trash even when prevented from playing cards.
EDIT: Way too many uses of the word "play" and its variants. To clarify, I would have the 5th card be put into play, and not prevented by Impulsion Beam's effect.
Good question. I agree that your option 3 was a good choice. I wonder if putting the card FACE UP on the deck might have been even better, so it's still revealed.
Option 2B: The revealed card remains in revealed limbo, but is available for selection during future Arcane Cadences (which would then leave a different card in revealed limbo).
If cards can't be played you can't "Play the top card of the deck," so you shouldn't get the card play from Cadence.
A revealed card that should be played but cannot is an interesting connundrum, and I would solve it the way you solve a limited card being forced into play when there is already a limited card in play, put it in the trash.
That is in no way official, since that rule is spelled out in the rulebook, but it makes sense.
I'm an agreement with anyone that says you would not be able to play the card from Arcane Cadence, as you can only play 1 card. Now what happens to the card is a mystery, i'd probably go with is goes to the trash.
"Play the top card of the deck" is the method of playing villain cards. Playing a hero card means putting a card from your hand into play. Since the card in question doesn't get put into the player's hand, but is being put into play by another card, I'm not seeing the reasoning for saying it would be another played card. The hero is not playing a second card.
I realize that the card says "play one" rather than "put one into play," but "put one into play" is the accurate way to describe what the card is doing.
It's possible I'm misinterpreting something here, or there may be a relevant ruling I don't know about. But this is how I see the interaction, and why.
Yeah, I think it's a really arbitrary technicality. It should be "put into play," but was likely shortened for word space. Besides, there's nothing else you can do with it. I'd say play it.
It's a card that's been revealed from the top of the deck. Arcane Cadence says to play it. If hero cards can't be played (which is the condition after the first card is played), it can't be played, so it goes back on top of the deck, above the card placed there by Arcance Cadence (because it was only revealed by Arcane Cadence).
Seems clear to me. 
What makes this unclear is that what Arcane Cadence says (play a card) and what the card actually does (put a card into play) are two distinctly different things.
Since there's precedent for the act of putting a card into play ignoring effects which prevent cards from being played, this distinction becomes important for this interaction.
It says it plays the card, that means it does play the card. No cards in Sentinels of the Multiverse says one thing and does another, they do exactly as they say.