Thanks. New best is 42, which is with 5 bosses (including end boss) and taking the hardest paths, but getting pretty unlucky on paths other than getting the option for 5 bosses. I would say the minibosses, including the dragon but except for the Slime Queen which should be 3 points, work well for 4 point nodes, but the only non-boss level that is as difficult is the same one from the first version with the three small green worms. The slime altar level is close, though, if it has a fire turret. If you could guarantee a fire turret, two shooting flies, and change to an actually-dangerous slime it would be purple.
Defiance is also way too easy to be purple, but it's special because it is the first boss level, and that's fine. I do feel like more variety in the first boss level is the number one improvement you could make right now, though; it's a fine level, but it's quite slow due to the worm and turrets all being very defensive, and it's VERY slow if you don't play it exactly the same way every time so that the shots on the turrets are planned out to ensure the worm dies after the turrets.
For hard levels, Acid Walls is very fun and appropriately labelled. High Noon Mania looks cool but I've never actually seen it in the game; in general levels with healing slimes seem exceedingly rare, which is fine in terms of balance. It would be a bit hard without the slimes I think, but not a good choice for purple probably, since it would certainly be the easiest (besides Defiance), and is mostly a gimmick level anyhow (once you know you should shoot a turret and jump over the edge it's more tedious than hard). Easy Tomb should be Medium, not Hard, Exploding Flies is weird because sometimes you get lucky and roll 1 fly and it just seems silly since it is then easier than Cowboy Duel. In general I'd say it feels like a medium or easy difficulty level, but the exploding flies take a while to learn the trick to, so it's probably fine as Hard, though 2 to 4 exploding flies (with the 2 on one side together guaranteed) would be better. Escalade Flies and Small room are fine. PachinkoFliesEasy should really not be Hard. It should probably be Medium but Easy would be okay, too. The actual Pachinko Flies could be Hard, though, again because of the gimmick.
The Goo is another level I've not ever seen in actual play, and it seems a bit hard but probably just because I'm not used to it. I especially wouldn't consider making it purple due to the ledge the player starts on; if it was a level I played a lot I would master jumping off that, shooting, and landing back on it to kill all the slimes regardless of species without danger. BiSphere is fine, but not particularly exceptional.
Three Pillars of Suffering is a bit on the difficult side, it could almost be a purple.
For Medium, there are a couple that should really be marked harder. I'm not going to go over all of them because Medium and Easy are kinda indistinguishable to me in terms of feel and both are stuff you try to avoid to get a high score.
Forgotten Moat is almost Purple. The main reason I wouldn't want it to be purple is because it's too similar to the three short green one level, just easier due to having only two worms and some flies you can use for cover. It sure as heck isn't medium!
Two long wavy should be Hard. Pretty much anything with the poison worms is a lot more difficult than the labeling seems to think; maybe there's something I'm missing in terms of fighting them, idk.
Bridge of Fire should be Hard. It can go really fast, but it can also be a deathtrap.
For Easy, the only thing I wanna say is that One Long Wavy should be medium.
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One option you might want to consider is adding a 5 point tier for the hardest purple levels (three green worms, worm tank, momma flies in descending order) and then upgrading the harder Hard levels to the now-easier 4 point tier. This would make the game between the hardest Hard level and the easiest Hard level smaller, and the same for Elite. You'd need more 5 point levels for this to work, though.