[Endoperez]

There are many items that speed up destroying castle walls as well. Gate Cleaver and Air Shaker, at least. Once you can storm it, it helps if you can use fliers to distract enemy mages. Also, it can help if you have fast, powerful units just before the gate that just dash forward, and more units just behind them so that they will get help as fast as possible. This way your units have a chance of getting through he gate faster.