Properly done out:
Setup: Play Tactician. Opponent, on a Tactician turn, plays 3 King's Courts and 5 Swindlers. He then plays Tactician and buys Messenger for Rocks and Mission. For the next hand, he plays 3 King's Courts and 4 Swindlers, Outpost, and Tactician, and the third he plays 3 King's Courts and 5 Swindlers, buying Messenger for Rocks. Total, that's 14 Swindlers tripled for 42 Silver in hand. (No Watchtower because another Black Market is just loads better.)
Then, we have a hand of 4 King's Courts and 6 Black Markets. So that's 3^18*3*42 ending Silver, 3^18*3*42/7*3^18*3*42 gains is a paltry 10^20....
Main issue really is X is different, because different cards are being used to reach it. If X was like 760 it would work... but the loss of stuff like Haunted Woods and Council Room might just be too great to bear.
FWIW I think you can do better with this strategy if you add golem (I think it's fine with no actual card draw) if you start with a hand of entirely golems you can play one hitting KC and X (swindler for the opponent, black market for us). Then use KC first on a golem again hitting KC plus 5X and repeat for as many golems as you have in hand. With a 10 card hand (tactician) this leads to (I think) 47 plays of either black market or swindler. Using coin token on golem should help increase the starting coin. Buy token on black market cause why not?
The number of golems can get up to 12 using save and overgrown estate but we still don't get anywhere near as high as stef/liopoil.
Also, buying raid is way better than ball.
One question: how are you trippling with each black market play? Isn't it double since each coin becomes a silver.