Mer-knight, Uncommon, 1g6r
Aqua. Soldier.
Attack: 10
As someone who's been playing the Aqua keyword a lot recently, I feel that this is too much for an uncommon Aqua. Right now, Aqua is well balanced in that the Uncommon and Rare cards with the keyword (which are necessary to see the excellent keyword effect occur) are either underwhelming in their effect/cost ratio or are simply too expensive to play them frequently.
Having so inexpensive an Uncommon Aqua would throw out that balance. It needs either to cost more or do less. As things are right now, I would probably take this card at its current cost even if it had zero attack just to gain the +5 wall +5 tower -3 opponent's stock on my following turn and having had another Aqua keyword in my hand up until I did play it.