I'm kinda sad to see this post un-responded to. I came around to the forum to see if anyone had much success at a Shard of Patience deck making use of Flooding, but have yet to find one, even after a search. I think the main problem is finding a fast enough deck that can put multiple creatures into slots 6-23...
Regarding your initial post, then: I think that something like this is a cool idea. HOWEVER, it sounds way too OP; at the very least, it should not produce extra water quanta, because the interaction between
and
would be way too strong, as you noted. Flooding already doesn't cost much, and as you proposed, it would be too easy to play this Hill/Mountain card earlygame along with Flooding to completely lock down creature decks, and Trident/Poseidon could stall, and kill many decks with this combination.
Also, perhaps this card could "lift up" creatures in slots 1-5, giving them some sort of Reach or something, but
creatures would suffer some sort of disadvantage?
All in all, I'd like some more discussion on this - I think it could work, given enough reworking, and make the special effects of Shard of Patience actually shine.