OK, so let's work on this analytically. What do we know and what do we need to figure out:
Unlocking Cosmic Omnitron
Need:
While fighting Voss, destroy both ships (Stalwart & Conqueror) in the same round
+ Mystery Condition
The Mystery Condition does not seem to be any of the following:
Team composition - Cosmi's been unlocked using non-overlapping sets of heroes - so it can't be something unique to a specific hero. [Has anyone unlocked Cosmi without having at least one variant hero on the team?]
Fight Location - Cosmi's been unlocked in both Megalopolis and Insula Primaris - so it can't be something unique to a specific env
What else have we mentioned in this thread…
Order of ships destroyed: I unlocked after taking out Stalwart first, then Conqueror worked and Chromium got it after the other order, so that doesn't seem to be relevant (which is good as it would mess up people using Savage Mana as you can't control the order it sends things to the trash).
Who does the damage / damage type: Probably not relevant, Cosmi's been unlocked after one hero destroyed both ships and after different heroes destroyed them on subsequent turns in the same round. I've seen a couple of reports of Savage Mana unlocks, has anyone confirmed an unlock with End of Days?
Single-Shot vs. whittling: I unlocked Cosmi after single-shotting one ship with radiant damage and plinking another that was at 1hp with a projectile. Other folks used Savage Mana to discard both at once. Powerhoud took out both ships after they'd been previously whittled down. Seems like this isn't relevant, unless I'm missing something
Voss's board: Has anyone unlocked Cosmi without having Voss's field cleared? I don't think this is relevant as Carlos said he'd gotten both ships and "Sometimes it was just Voss and the ships, other times there were minons." but do we have a data point of someone actually unlocking while Voss had other cards in play?
Voss's state: I unlocked him with Super-T Warrior side up (as did others who had been taking out all the minions). Has anyone unlocks Cosmi with Voss in Warlord state? Voss had 81HP and 7 cards in his trash at my unlock.
Active Hero state: My unlock was triggered by RC Wraith doing 1 point of damage to the Conqueror. Wriath had 7HP at the time.
Story possibilities: Cosmi's bio says that a "mysterious cosmic entity" rocked Tachy's lab with "cosmic rays" which "gathered the many technological advancements of the lab together" and "bound them all together with wires and connections of pure energy." We know Tachyon's not required, but could there be another clue here? Might destroying the Quark-Drive Translocator also be relevant? Seems unlikely, but I'm trying to search for what we might have missed
Anything else?