In general - Try and 'draw' every round for as long as possible. Then once you HAVE to start winning you want to win with a single beefy guy in each row to minimise the damage to the castle.
Specific tips:
-Prioritise Bat Curse in every book slot early. This is a way of "banking" money/power so you don't get too powerful and start winning rows. Only use the curses after your side is dead.
-Buy every single mauseleum (gold generator). You can never have enough. That's how you keep rolling late game for whatever crazy strategy you are chasing.
-The maximum damage your single unit needs is only 9 to 1 shot everyone. Even so you don't nessecarily want to hit that cap too early in case they completely roll over the enemy.
-Use spy liberally early-mid to try and match each rows power in order to 'draw' or be overrun (and then bat curse).
-Sell all your buildings on the final turn. They don't do anything for the final turn after all
