3/5 - I imagine the idea is far from new (especially seeing as there's a Yu-Gi-Oh card that does almost the same thing), but reducing all creature damage to zero is a nice twist. Gets around the damage reduction nicely, but it doesn't have a means of allowing quanta to be drained. As you said, that's not a hugely common occurence, so it seems a little moot to have a card specifically countering it, but your card would work very well with Devourers, so by failing to properly counter that second effect, it itself suffers. The idea is done really well, though.
Name: Dilatant lake | Dilatant moat
Element: Entropy
Cost: 2
| 2
Type: Permanent
Text: All creatures which do not deal damage take 1 damage. Stacks. | Your opponent's creatures which do not deal damage take 1 damage. Stacks.
Notes: A Dilatant fluid is one such as cornstarch in suspended water. If you apply a large amount of force to it, it acts like a solid. Otherwise, it acts like a liquid. Creatures which don't deal damage to their opponent are attacking so slowly they begin to sink, but ones which do deal damage get make it across just fine.