For the sake of clarity:
Frostmare is affecting its own summoning cost, which must be paid before it hits the board. If opponent has Kris and you have nothing, then Frostmare will cost -2. If opponent has 2 allies and you have 1, he will also cost -2.
Wild Berserker gets his haste after he's on the field, so he counts towards number of allies, so opponent would need one more than you on the field for him to have his haste.
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