Alright, finally got around to testing on my pc. Firstly, the score and death plane bugs were persistent across all tests, including firefox on arch linux, and firefox, chrome and edge on windows. On the itch.io app for both oses, game fails to boot with this error message: "The following features required to run Godot projects on the Web are missing: Cross Origin Isolation - Check web server configuration (send correct headers)". Seems like its an issue with the way certain godot versions export to html, from what I could find. Out of curiosity, which version are you using? Anyways, another weird thing I encountered (on all browsers) is that with some larger chains, pieces will get flung violently, sometimes even offscreen (which causes the game to lag significantly). Also, is there some sort of list of pokemon in the game already? I'd love to look at that so I don't make redundant suggestions. For suggestions though, Ralts and Stonjourner are the ones I'd want to see. Now that I've played it with audio, I can say that the music selection is great (and the combos are much more satisfying). In terms of nitpicks/suggestions, I'd love to see the ability to rotate pieces before dropping them, and a "hard drop" to drop pieces with more force. Both of these are in Suika Shapes, and I think they'd work quite well here. I wish the pieces dropped from above the red line as well, since once you get close to the top it's quite annoying to build. Different background images could be nice. The transitions between songs are awkward as well, could use with a shorter blank space and/or crossfading. Another thing worth noting is that on the chromium based browsers I tested (chrome, edge), physics seemed smoother and more exaggerated than on firefox, not really sure why. One more thing I'd like a lot is a standalone executable (or at least downloading through the itch app working) as loading times are very long every time I want to play. Source code would be fun to mess with too, but that might be a bit tricky honestly, and you might not want to release it either.
Anyways, sorry for the wall of text! I really like what I've seen of this so far, and also happy with how active you've been with it! I'm happy to help out with anything (if you're interested) as well.
(Edit: Just looked at sandbox mode and saw that Ralts is already in, so I'll suggest Crobat instead)
(Edit 2: Would also love to have a "Playlist" like option for sandbox mode, where you can select multiple pokemon for each tier to be randomized between, or a blacklist option to remove pokemon from the random selection (functionally equivalent), maybe even have it for the music too. Seems pretty difficult and definitely not necessary, but could be pretty neat imo.)