So this is a little complicated, but totally doable in Gauntlet.
The whole crux of this is to trick your opponent into playing a Site, but because the AI in Gauntlet doesn't play them - we have to give them one.
Here are the critical cards:
Highway Devourer (in Market)
Yushkov, Brutal Tyrant (in Market)
Fall To Ruin (in Market)
4 x Wasteland Broker (in Deck)
4 x Cobalt Coin (in Deck)
4 x Jolu, The Gift-Giver
This is a link to the rest of my deck, but it can really be any control deck with Fire/Justice/Shadow cards. Mine is a Stonescar Grenadin sacrifice deck (mainly to get enough cards in my graveyard to trigger the Fall To Ruin and feed Yushkov)
The rough outline is as follows:
1. Get to a stalemate in Gauntlet while earning Power/Influence.
2. Control the opponent's side by removing units - try to keep them manageable while building up your forces.
3. Wasteland Broker - Yushkov (puts 4 into deck)
4. Wasteland Broker - Fall To Ruin (puts 4 into deck)
5. Wasteland Broker - Highway Devourer (puts 4 into deck)
6. Play Yushkov and Jolu - to give your opponent Yushkov.
7. Whatever you swap with (make sure it will not kill Yushkov) use it to attack.
8. Yushkov hopefully killed that to build its mastery while also triggering the Cobalt Coin - cast Inferiority Complex on the opponent's Yushkov to make them "reckless".
9. Feed a reckless Yushkov grenadins until his Mastery triggers and gives the opponent a Korovyat Palace draw.
10. Play Highway Devourer and your opponent should have played the Palace on its subsequent turn.
11. Play Fall To Ruin to wipeout your opponent's side (having 12+ in your void to save your critters)
12. Highway Devourer kills the Palace
13. Kill your opponent.
Achievement pops when the battle ends.