this is the best deckbuilder i've played in a while. I love the amazing and ingenious twist on the old classic.
my endless ramble that is my thoughts (u don't have to read this):
1) I think there would be a cool roguelite element if you added different starting characters.
ideas/examples:
when you first start, you are a basic duck who begins each run with 5 basic tiles
after you beat pond ruins, you unlock armor duck who begins each run with 2 shields and 3 basics
etc. etc.
if you want to preserve the roguelike element, then you don't have to, but i often find that with roguelikes like yours, it feels too luck-based to beat the game. if you added a character unlock system, it would be a easier and more interesting game as you can make fun combos with different starting decks
2) I think the second boss may be too overpowered, because if it makes a match with 3 unharmed shield tiles (which is 80 percent of its deck) it matches twice, once for the original match and again for the match of cracked shields after all the tiles in the match take 1 damage. you could change this by adding more diversity to his deck, instead of 4 shield + 1 heal
3) the trade offers are a bit much, because they often trade for a good tile, but at the cost of 2-3 pretty good tiles, which is not a worth it sacrifice.
4) maybe for the last area, add a huge possibility of routes with maybe a elite only route that faces you against elite after elite, for skilled or very lucky decks who want to go for high scores and high rewards. you could also add mini bosses and a final boss