The damage component of the unlock is almost certainly 'at least 20'.
I have two logs, in the first, XPWAA did nothing except use Rebel Yell to deal 18 damage to Villain targets. It failed. In the second, XPWAA did the same but with 20 damage. Success.
I don't know about the helping other heroes out component, but dealing 20 damage or more seems to be the key.
Logs are attached with their name indicating AA's damage amount.
Edit: I should say I also have another failure where AA did 19 damage, but he was using effects on other heroes in that attempt. If that log ever seems like it will be useful, I'l post it.
For now we should probably concentrate on seeing which powers AA is allowed to use and on who, while also dealing at least 20 damage.
Now that I know my fail log was a bug, I do now wonder if it's as simple as having Argent deal 20 or more damage in a game, with winning also possibly being a requirement going from QuirkyDM's post.
I thought so too, but meemitone has a fail log on Steam (post 161) where AA does a heaping pile of damage and it didn't get the unlock. That might be a good one to pore over for potential riders or "thou shalt not" conditions… Unless it was also bugged like Jeysie's was.
In my unlock, AA did nothing but pass until the last few turns when he set himself up to do 20 damage. So I'm certain the missing condition is one or more "must nots".
Failed unlock, so one of the "must nots" must be in here somewhere. In addition to dealing damage, AA healed himself, destroyed Environment cards, and gave himself additional power uses. Other charcters made him draw and play cards, redirected damage, and powered up his damage.
Just got him. Legacy, TLT, Xpwaa, Ra, Parse vs Baron in Zhu Long. Argent definitely dealt over 30 damage. Used his power to once boost Ra. Only song used on someone else was syncopated onslaught. It might have something to do with deal the damage in a certain number of turns. I dealt the 20 in 3 rounds.
has AA heal with both Vernal Sonata and Rhapsody of Vigor.
So the only red cards we have are Sarabande of Destruction and Syncopated Onslaught.
Could it simply be:
Argent Adept (any form) is on a team that wins a fight. Argent Adept must have dealt at least 20 damage and must not use the perform effect of Syncopated Onslaught to increase damage of other Heroes.
or
Argent Adept (any form) is on a team that wins a fight. Argent Adept must have dealt at least 20 damage and must not use the perform effect of any Rhythms or Harmonies on any other Heroes.