An okay game, but has its share of problems
And no, I'm not here to complain about the Phantos. At least not in the way others are.
First thing I noticed is that reaction time is a statistic. Why the heck is a game mechanic part of the character differences? Seriously, there's no reason to have that change by player character.
Second is that mouse control on laptops is somewhat tricky, especially on those who have the buttons close to the pad. Not all of us have desktops/plug-in mouses, and Newgrounds as whole needs to realize this. Having the power-up close to the controller button is asking for the tracker to violently change position. It also causes unnecessary use of power-ups, as most pads left click when touched in a way similar to the one used when shifting sliding position. Maybe the power-ups could be assigned to the space bar next time?
A third issue is that the difficulty is far too unbalanced. On the one hand, you have the easy mode where you can basically blow through the game as Bill, and maybe one or two of the bonus characters (that Bonus boss is very disappointing by the way; not that he should be insane, but he doesn't stand a chance dancing for 30 seconds before any kind of an attack). On the other, you have a super hard mode with a deadly homing missile that just lasts through the one hardest stage. You see the problem here? I hope so.
The fourth is the Phanto's mechanics. This is not about it tracking you, per se, or whether or not it's optional. It is, and I realize that, but the reward is practically non-existent, especially since you lose points to change anything in the middle of the game. Said reward is far too little to compensate for the middle layered, road-blocking demon that is Phanto. Seriously, I had to repeat levels multiple times just because he seems programmed to appear in the middle of narrow corridors right before the boss. (Final level especially, it's as if you were payed to make that level a hallway.) I've read your excuse for a walkthrough, and "I made him to be a d*ck" is like admitting "5 people will actually deal with this fairly large part of the game". I'd say allow the player to change some of his attributes to their idea of difficult, and make the reward a bit sweeter or more bitter depending on what they change.
Also, just as a small note, but a sufficient problem: the way in which the player moves. Spot-tracking is terrible to use, most noticeably during a key run. If I want to hope to loop around a projectile in a tight spot, like Phanto or a hammer, I'd have to slow time just to do it. The character follows mouse position devoutly, which means instead of going around, it dips, then comes right back up and dies. Along with this is hitbox cropping. It's only really noticeable on large characters like Kid, where just coming close to a wall causes death far too often, and sharp turns like those needed in the last water stage are nigh impossible to make.
I do hope you'll make another of these though, it's a nice game idea. Just far too blunt to be taken seriously.