It's also not: vs. the Ennead in the Final Wasteland, let the Environment remove Ra from the game, after dealing AoE fire damage to all non-hero targets.
Data: Legs, Fanatic, Scholar and base Ra vs. The Ennead in The Tomb of Anubis. I tried the Ra does nothing strategy. Won the game but no unlock. Not really surprising but it had to be done.
Also, with thanks to Parse, not:
vs. the Ennead in ToA
Deal 1 target 10 irreducible damage
Deal all non-hero targets at least 4 irreducible damage
and incap Ra.
This is just a guess but shouldn't the unlock come from Horus of two horizons since that would be what he was before he went to recruit the ennead?
Maybe? But I'm unclear on that point, since Setting Sun Ra is much more visually similar to the original, and the ARG comic shows him as pretty much regular ol' Ra. I always associated Horus Ra as being part of just that particular event, and then he went back to doing his normal Ra thing.
Magic 8 Ball says: Cannot Rule Out.
Yeah, I haven’t listened to the Letters Page episode about Ra yet, but I kind of thought that was like a temporary ‘wandering in the wilderness’ form rather than his ongoing look / ability...
I was going to test some stuff with Horus of the Two Horizons. I seem to recall hearing in The Letters Page that the conception of Ra's forms was "new day, midday, evening" and thus, each gives way to the next.
maybe it’s three games then?
In one of the episodes of The Letters Page(I'm not sure witch, I think it was an interlude), C and A did mention that most characters will have a costume change once in a while, but they then normally return to their standard costuming after the special event passes or whatever. They even used Ra as an example, saying he did get a shave and return to his normal costume once he regained his mind and power after the Horus of Two Horizons events...
Not sure how/if this will key into the unlock, but just thought I'd mention it.
Data: Ennead in Tomb vs TLT, OX, Knife Rogue, and Ra Horus.
Tried winning with 2 Solar Flares in play. No unlock.
Relatedly, I just tried self-incapping Horus Ra with two Solar Flares, Imbued Fire, the Staff, and Flame Barrier in play. That was 20 self-damage just off the Solar Flares...
I've been running Ra (or Horus Ra), F5 Legacy, Omni-X, and PW Argent Adept to help Ra do all the things, vs. Ennead in Tomb of Anubis, and I'm clearly missing something. Team comp? Villain? Environment? Many of the Fall of the Variants unlocks required a particular environment. And since we don't have Ft. Adamant yet... I'm at a loss.
I think if I give this another shot tomorrow I'll make sure a Fanatic is on the team.
Could it be something he CAN’T have in play like his staff?
Also not:
Defeat the Ennead with no hero except Ra dealing any damage.
Ok. I am a little.frustrated with this one. The letters page (listened both to Ra and Ennead episodes) indicates Ra joins forces with Anubis and the defeats the Ennead before taking them to fight Oblivaeon. There is no mention of any other hero or anything.
I have defeated the enyire Ennead with Anubis in play and multiples of Ra’s ongoings and got nothing.
My only oyher guess is to go through Ra’s entire cycle. Losing to the Ennead and then making sure to encounter Ammit (not sure if I need to win or lose there so maybe do both?). And then go back and beat the Ennead.
Well I guess I wl start trying that stuff, but it feels like I am grabbing at straws.
If this unlock involves the lead up to their final battle against Oblivaeon, than shouldn’t Ra be leading the team against the Ennead. After all, it was Ra that went to convince the Ennead to fight. And since this game isn’t 1 hero versus the villain I think Ra would have to be the one to defeat most if not all of the Ennead to simulate it was Ra And Ra alone who faced the Ennead. And since a battle like that would take a lot out of Ra and we know Ra succeeded, I’d imagine he would need to be low on health in the end, maybe below 10 or even as low as 1.
Fanatic was mentioned as well
No go on the cycle theory for me. Maybe it is something obscure like Ra cannot gain life…
The problem with the cycle theory is we already had to do part of it to unlock his first variant. I doubt we would need to recreate it again. Using his variant may be part of the unlock though.
You know that it’s traditional this time of year to give gifts, perhaps a hint could come from on high 
It hasn’t been a week since release so I doubt a hint is coming yet.
I have already had Ra defeat every member of the Ennead in a game. Maybe ypu need to do it and have Anubis in play at the end of the game.