Recently we played on a Tunnel board, and i happened to hit a 5/2 opening. I bought a Vault.
My second buy was Squire, the only 2$ in the kingdom. I only bought one more type of action card, and no other Squire.
My opponents bought Tunnels like crazy. They had a reason to do so, because from turn 3 on i played Vault almost every turn. The one time i did not, i bought my (one and only) Tunnel, but that was late in the game. So my question to you is: What other cards synergized good enough with Vault to make me (almost) ignore Tunnel and win with this strategy?