Well, balancing such an ability might be hard but we can always look at the most similar abilities. Possibility to use the ability many times makes it stronger, so to be balanced it should be less cost efficient than those abilities:
Fire Nymph / Red Nymph
Rage
+5 / -5
Rage
+6 / -6
Earth Nymph
Petrify
+0 / +20
6 turn stasis
Owl's Eye
3 damage to target creature
These are the most similar effects I've found, giving a repeatable ability to change a creature's stats. It seems the ability to lower hp by 3 costs 2 quanta, while ability to increase attack by 6 costs 4 quanta at the additional expense of 6 hp (or just 6 damage for 4 quanta if used offensively). So it's roughly 3/2 stat point per quanta.
I guess an ability usable multiple times per turn should be roughly 1.5 or 2 times less efficient, so let's give it 3/3 ratio. So if the ability is to give (or take) on average ~3 attack and ~3 defense it should cost 6 quanta... quite expensive, but it's a very versatile ability and if you have a lot of
it allows you to eg. kill all opposing creatures, or buff an army of scorpions, buff Deja Vu, creatures with dive etc...
or make it change stats by an average of ~1 and a cost of 2... or change a random stat (either attack or defense) ~3 for 3...
I hope this helps to balance the card. I don't guarantee my calculations are worth anything, especially because there are such factors as - increasing attack, decreasing attack and decreasing hp should be more expensive than increasing hp... but still it's the best I could think of for now.
