Since this card is a creature, I'm assuming that having multiples of these guys out would not cause the effect to stack then, correct?
In either case, I don't want to say that this card is broken, but the idea of possibly disabling shields could be a cause of frustration for many people, as this might be able to bypass cards like Wings or Gravity Shield (since the defensive 'active' ability of the shield is canceled). If it does stack, then Entropy would be the most effective element for both CC and PC, as the ability to basically waste quanta for an opponent's creature could be devastating (an Otyugh being unable to eat, or a Nymph losing its chance to use its alchemy ability).
Also, how does this affect pillar and pendulum stacks? Does the entire stack just fail completely in generating quanta? Or does it only affect 75% of the pillars/pendulums within the stack itself?