Instead of making it have a symmetrical effect that is terrible to build around, make it something like this (but probably change the amount of power gained):
For each card Burning in the opponent's hand, this card gains +10 
permanently.
#Buff Guivre
sleek mason
tacit yarrow
Make it a play abillity, this would remove the issue of it only dealing with 2 cards
sleek mason
True
tacit yarrow
This should also be applied to all 'burning' cards, as they make offensive burn worse to use than it already is