Tome of Water, Uncommon 15g
Enemy stock -2N
N=Aqua in hand
if Moat in hand >0
The stock reduction seems rather extreme for an Uncommon card. Aqua as a keyword is populous enough that it's easy to have 8 in hand, meaning that this card can easily destroy as many as 48 resources at the cost of only 15 gems. That's in addition to the card's other effects, including the likely stock reduction from the Aqua keyword itself, an effect which is almost guaranteed on the next turn as well due to the summon.
This seems like it should be Rare as presented. Otherwise, the stock reduction needs to be capped, or have N= Aqua on hand -4 or such so the reduction only starts counting with the fifth Aqua card.