OK, I just got the unlock, and I can definitively say that it doesn't have anything to do with Powered Shockwave – that was the one card in Unity's entire deck that I didn't play the entire game. I'm pretty sure now that it has something to do with destroying Supply Crate (or some equipment), bringing out a bot, then putting a bot back in the hand using Scrap Metal, because all of those happened both on my "unlock" turn and on your "unlock" turn.
I tried to duplicate your successful run exactly. Same team/conditions (Visionary, Grandpa Legacy, Unity vs. Ambuscade in Freedom Tower). Just like you did, I went through Unity's deck methodically until I had just about all of her bots out, as well as a bunch of equipment. Along the way, I played/used every card in her deck except Powered Shockwave – I was saving those up to use at the end as my attempt to finish the game like you did.
I wanted to set up my "unlock" turn so I could do what you did. (Destroy a Supply Crate to draw cards, play Powered Shockwave and Scrap Metal, use Workbench to play a BeeBot, then use Scrap Metal to take the Bee Bot back in my hand, and possibly, get the environment to play Supply Crate for me right before Ambuscade's turn.) So, with 90% of my setup ready, all I did on that turn was the following, never expecting it to do anything:
(1) Kill Ambuscade's cloaking device with Turret Bot (The only card he had in play.)
(2) Play Supply Crate and Scrap Metal (There wasn't one of either in play yet)
(3) Used Bot-Hack to destroy Supply Crate and play Bee Bot
(4) Wasted a bunch of bot damage on a still-invisible Ambuscade
(5) Used Supply Crate to put Bee Bot back in my hand (intending to play it next round for the "unlock").
The environment didn't play any additional Unity cards (only one-shots were left in the deck to be played).
When Ambuscade's turn came, he flipped, and I immediately got the unlock. So it happened not only without playing Powered Shockwave on that turn; it happened without playing Powered Shockwave at all. I put a more detailed breakdown of the turn at the end. (Since I'm on iOS, there is no log file, correct?) But for now, here's my current theory:
Unity must be on the team. On Unity's turn, she must destroy a Supply Crate (or possibly just "destroy an Equipment"?), put a Mechanical Golem into play, and put a Mechanical Golem back into her hand, all in the same turn. (Plus possibly an additional condition like "She must have X bots in play," or "She must have Y Equipments in play," or "She must have played X, Y, and Z cards at some point during the game.")
DETAILED BREAKDOWN OF UNLOCK TURN:
Ambuscade: Had just Cloaking Device in play
Unity:
Cards in Play at Beginning of "Unlock" Turn:
Bots: 13 (All except one Bee Bot)
Equip: Pylon (x2), Volatile Parts, Workbench
Cards in Hand: 18 Deck: 2 Trash: 3
Start:
Turret Bot does 5 buffed damage; kills Cloaking Device.
Play:
Supply Crate (draws Hasty Augmentation)
Scrap Metal
Power:
Bot-Hack: Destroy Supply Crate to bring out Bee Bot
Draw:
Supply Crate (x2) (drew last card from deck, and reshuffled deck)
End:
(Bots all direct attacks at Ambuscade; do zero damage – even though Cloaking Device was just killed, he's still invincible/unhittable until the beginning of his turn.)
Use Scrap Metal to put Bee Bot back in hand.
Environment:
(Nothing – with only one-shots in Unity's hand, there's nothing to be played; I ended up discarding two one-shots)
Unity at Time of Unlock/Beginning of Villain Turn:
Bots: All except 1 Bee Bot
Equipment: Workbench, Volatile Parts, Construction Pylon (x2), Scrap Metal
Cards in Hand: 20 Deck: 1 Trash: 2