Kamikaze
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Let me remind you, there was also mention of materials for the amulet. So that in the first round of the battle, griffins attack someone else, and not the vampires.
Massive slowing in the first round allows you to curse the griffins in the second round, which they are quite susceptible to. Adding spells that increase the damage of vampires, as a result of their ability, is quite effective.
Of course, there should be a sufficient number of vampires remaining during the battle, so you can also enhance their defensive properties.