First, welcome to the forums.
Second, go swallow a bottle of bleach!
j/k
In all seriousness, you are a pretty talented game maker in terms of the production value of your game. You have a lot of things going for you, and I think if you shift your design away from being a hardcore trigger trap game and more towards a platforming game you could possibly have one of the more popular fangames on twitch tv.
I'm going to leave some feedback here on various parts of your game, you can take it or leave it.
Let's start with bosses. I see you took my suggestion to switch off of bullet spam to the immunity frames, which I think has made the game better overall so people are not forced between using autofire scripts or straining themselves. Now that you have made this change, you need to examine the individual bosses to make them a better experience.
I have not seen all of the bosses since I haven't reached the end yet, nor have I played 1.4 as of typing this because I'm at work and it just came out.
The slime boss in the Dragon Warrior area, just about where he needs to be except for his one attack where he summons the metal slime that shoots the rockets. The current version of the fight with this mechanic creates impossible to dodge scenarios because the missile stays on the screen during the transition into the next attack. You should consider not having the next attack start until the missiles are gone to avoid RNG luck determining the outcome.
The boss in the mine area who shoots the ice, he needs A LOT of work. The only way I was able to get through him was to download the older version that let me autofire him. Some of his attacks needs to be examined. The attack where the ice comes from under you and lifts you up, 4 times is too many because it creates RNG situations where you don't have enough room to avoid them. Make it either 3 attacks or make the platforms smaller, or both to avoid unavoidable death.
The attack where he summons 3 ice crystals and the wind blows you around, you need some sort of a visual indicator to let people know where the wind is blowing or shifting because you just start flying around with no visual queue and with the random intervals of wind shifting it is a bad mechanic.
The attack where he throws the giant ice crystals that explode can create unavoidable death because of the amount of room you need to dodge them all. He needs to throw less of them or they need to be smaller, or make them fall from the ceiling over the players location instead to remove the possibility of RNG death.
The Dark Kid boss fight in the mine where he shoots the red and blue balls, I thought the older version of the fight (30 something hits?) was much much better than the newer version with 75. I was forced to go back to an older version to get through this one.
The 2-D shooter Area
Personally I hated it, I don't think it should even be in the game at all. It looks like a really bad attempt to do what Boshy did. Don't try to copy Boshy, we've had enough from other games.
If you MUST have it, then consider making major changes. Only a few of the weapons are remotely useful, Magnet, Option, Slicers, 3-way, Spread, the rest are trash and make the game harder remove them or make them more useful. The save points often times leave you in a position of being shot from behind as soon as you respawn, this is bad design. Find a way to let the player spawn without a spray of bullets flying up from behind them. Also too much RNG in the first half of the section where you get swarmed by a million guys.
The boss, just a complete train wreck. Too much RNG. No visual indicators of what attack is coming, or the spinning beam of death that randomly switches directions needs something to warn the player. He has so much life combined with the stupid RNG makes it so only the slicer or the Spread with 2 options can kill him. There's no way a player who is not a direct descendent of Jesus will kill this guy through other means.
In the Dragonwarrior area, there is a screen with moving blocks that you can not jump in. There should be a save point on the easier setting halfway through the room after the second monster going up and down. The blocks don't sync up half the time and this area is very tedious in its current form having to start at the bottom each time.
The area I haven't done yet of which I have only seen the first screen involved jumping on a platform to switch directions. I don't even want to play this to be honest. Probably one of the most annoying and unfun mechanics which is why I have avoided it until I absolutely must, and even then I may just stop playing here.
The area where the flying guys are shooting spears at you...WTF is this? It's just RNG shit, come up with something that makes more sense. I got through it but it felt unsatisfying because of RNG.
For some balance- some things I thought you did well.
The Megaman area before the 2-D side scrolling area was a good example of good platforming with not a stupid amount of trigger traps.
The Kirby area where he chases you, thought it was pretty well done, and again had no real trigger traps.
The platforming in the dragon warrior area, and the areas with the heads that spit barrels was decently designed.
This shows me you are capable of making good platforming without the use of trigger traps, this is what you need to do more of. You have a LOT of potential, we don't want to see you wasting it. I'm sure I have more to say but my lunch break is over.
I really hope you will take the criticism seriously because this game is going to be forgotten in 2 weeks but it could be a game that reaches Boshy level popularity.
