This isn't so much a neat interaction as it is a hilarious situation I'll probably never see again: Colony Dancing.
It was a Platinum/Colony board with Dominate; also Tomb, Sauna/Avanto, Crown, but without a readily usable source of + Buy (I think Spice Merchant and Ruins from Death Cart were the only possibilities?).
We both went for Sauna/Avanto, mirroring almost identically, trashing down to overdrawing decks capable of hitting at least $14 every turn and then splitting the Dominates 3-3. Then, with scores basically tied, we naturally followed the well-known Penultimate Dominate rule and started Colony Dancing. We split the Colonies 3-3, and then started Duchy Dancing. Both our decks started stalling out, with mine failing first, giving my opponent the victory, though it really could've gone either way. Alas, I doubt I'll ever encounter such a bizarre, amusing mirror game.