balancing mechanism 1) the basic card deals damage to both players, dis-swaying the player himself from using a rainbow or using quanta generating cards while this is in play. the upgraded only damages the opponent, but has an increased cost relative to the basic for this change, despite being upgraded.
balancing mechanism 2) low damage against most monos/duos, if the opponent is not going to use quantum pillars, this card is less effective than a creature or creatures of relative cost. this functions similarly as black hole, the only anti-rainbow focused card, which does little against monos/duos but thrive against rainbows. reverb can do damage or dissuade the opponent from using nova/immo/etc, while black hole removes quanta and generates healing. dissuading vs removing i considered a wash and for damage vs healing i felt damage would be more useful, so the cost of this card was increased relative to that of black hole. (it is also important to highlight that black hole removes *and* heals, while reverb will do damage *or* dissuade, or a little damage *and* dissuade)
balancing mechanism 3) the opponent will be aware of the effect and can withhold use of nova/immo/etc until the effect is over, or take the damage and use the quanta if they feel it is worth it
balancing mechanism 4) three turn duration is in line with phase shield, and one turn longer than SoSac, with aether being a quanta-hungry element, the costs are not trivial to maintain upkeep of this
potential adjustments could be:
capping it at around 20 damage per turn
reducing the duration by one turn (doesnt feel like it would be worthwhile using if so)
have the upgraded continue to deal damage to both players (would result in the upgraded card's cost also decreasing)