Enemy imp's Golden statue made with Aureate Monolith locks mana in level 3 Heart of Gold
I was with 14 imps and no other thing locking mana and when I tried to make more imps I was receiving voice alert, that I didn't have enough mana to lock. Tried to destroy all my imps and even with 0 imps there was mana locked by imps. Where, how? I discovered that, when I threw enemy imp's golden statues on the colossos forge and they disapear, mana locked was released. Some how, the statues are count as ours imps, locking mana as they do. (Sorry the english bad writed, I am Brazilian)
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