Wow, there's a huge variety of gameplay here! I love that the characters have different moves and the fact you need to charge up to use your abilities gives your game real depth. The grapple vs flying was a clever way to make the controls of mouse and keyboard distinct as well as give each character unique movement.
Choosing from multiple stages was a nice touch, although perhaps they could have differed in ways other than just cosmetic (e.g. the positioning of the platforms). The lava rising from the ground is also a great addition but perhaps it could have been communicated to the player when it would happen so the player doesn't feel cheated by it.
These are minor nitpicks though, the game is really solid and with some graphical polish I could definitely see it on the marketplace. Congrats!