This seems more like a mobile game to me. There isn't much to do gameplay wise besides moving left and right. Although the floaty physics could lead to some interesting trick shots, there isn't much of a reason to stick around after 3-4 levels. You should also make it clear what the controls are. WASD is fairly intuitive but I couldn't find a pause button or anything and just had to Alt-Tab out to quit manually.

The ramp at the end of level 2 was cool, but I somehow skipped past the hitbox for the end of the level with it and just kept going for 5000+ points before I threw myself off the edge. Speaking of which, I don't see the purpose of counting points since the levels seem to end at a specific distance anyways.

The floaty physics also allows for some cheese if you can tilt yourself off the edge and then come back. This lets you gain height for some reason. I can't do this consistently, but I've had it happen.

I think that as is, the game is almost unsalvageable. The concept itself has already been covered by the "Run" series, which are old Flash games, and I frankly think that those have better level design as well. However, I do think that the physics would be interesting for a 3d platformer. I think it would be interesting to give the player agency over all horizontal movement, with the limitation that they have to exploit the environment and the floaty physics to gain any height.

I think this is an interesting concept, but it needs a lot of fleshing out. Speaking as an intermediate chess player, the balance is also a bit out of wack.

First of all, the map is way too short. Your ability to win is dependent mostly on the starting army giving you something that can defend against a Queen. To make every run feel more different (which is what you want when you're going for a roguelike game) you need to make a longer map, like in Slay the Spire, Peglin, or Inscryption. I think you also need more relics. Since there are so few and you get to pick from a selection, you often end up with the same relics every game.

Also, the Immortal is completely busted. If you ever get two of them it's pretty much an instant win since nothing can take them if they stick together. They also feel really bad to play against since no chess principles work against them. Technically you can pin them to the King but even that doesn't really do anything since you can't add attackers or remove defenders to capture it.

I also think the graphics could use a bit of work. The menu and map look a little bit flat, but some simple animations for mouse-over and clicking could bring it to life.

Other than that, I really enjoyed the other piece designs. The Cardinal is a natural upgrade to the Bishop, the Pegasus is a natural upgrade to the Knight, and the Viking and Berserker are fairly interesting additions. The Portal Mage is a pretty weak piece, but it enables cool tactics sometimes (I would remove it from the starting pool though). I also liked the Pawn buff to account for the terrain. My only real complaint is that the Turret feels relatively weak compared to the other upgradeable pieces.