This combo seems pretty darn strong to me, and it even makes a good opening if my experience with it means anything. We all know Masquerade is a great way to quickly trash early cards AND a good card for Big Money. Having a Market Square in hand during early trashing is fairly likely, so you can trash Estates/Coppers while gaining Gold without actually hitting $6 (Or if you hit that awkward Silver + 4 coppers and want to trash but also get a Gold, hey, here's a great situation for Market Square). It's a good way to get a 'Tunnel effect' going faster than Tunnel ever could, and to make matters better, Market Square is a nonterminal source of +Buy. Any thoughts? I guess it has the drawback that you don't really need to trash the Copper for BM, but perhaps you can use it to transition in to an engine and only keep the good money. At any rate, I like it.