"Ashes' Will" - "The Last Soul" [2nd campaign, 1st mission]

The manual (it's located in the "fun documents" folder, along with the skill wheel) contains a lot of useful information about the game mechanics. Bees push back a stack by 0.6 attack points; the frequency of the hive's moves depends on the hero's spell power, and the hive's initiative is 10 + 0.25 * spell power. The hive's initiative should be noticeably higher than the initiative of the stack it will be holding, and you should also keep mana in mind.