Ple-Sen
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I think it's better to send only the flying units up, not the whole group. Also, it's not a given that no one will die in the Tower. According to my calculations, you have 46 stones + a staff with 8 charges + a vial of dragon's blood. That's 5-6 resurrections, depending on whether you can use the staff to cover part of the cost and the stones for the rest. And you only have one chance to resurrect the shaman himself, using the vial.