The castle is very unpleasant – there’s practically no one to fight with – only units 6 and 7, and even they aren’t ideal. I never mastered the tactic of raising units – thank goodness – in my opinion, the most winning strategy is to build a 4th-level magic tower around week 3-4 and use Armageddon against the Efreet. Then you can break through anything and take Utopias if you really need to – before that, it’s completely useless – and Devils aren’t cheap either. Until you have Efreet, you can’t break through anything significant or accumulate enough for Devils – but overall, even with a focus on fire and Armageddon, there aren’t many chances to win – I would develop five fire Warlocks for Armageddon and try to pressure the enemy with them (starting with smaller, Warlock-based units).