Warlock – “Cultist” [Campaign 4, Mission 3]

and I capture two castles in 5 days, defeat the red player, and then the blue players come and defeat me with such ease, as if I were level 1.

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Does anyone know how many blue castles there are?
Because I capture the third castle and don't have time to attack from the other side before the end of the week, and my army is at zero.