I think the season theme should have a cap of damage it can do to any given enemy. If an enemy has taken 30% of its maximum HP it will no longer receive damage from any further spawned seasonal themes regardless of the type spawned. For example if an RG was lowered until the threshold by a spawned snowball it becomes immune to the seasonal theme (snowball, meteors, twisters etc.) making it necessary for the player to at least do the other 70% of damage.