Shotgun Raiders (Steam key).

http://store.steampowered.com/app/510330/
Introduction
Shotgun Raiders is a 2d fast action platform shooter.
Inspired by the easy controls of classic mario, limited gun angles of the good old arcade shooters, and level crafting.
This is a bloody 4 player local party game with file access to import your own characters, share created backgrounds & levels.

Features
Trading Cards!
Premade levels.
You can choose (original levels or player created levels)
2-4 player battles or play against ai on easy medium or hard.
You can create your own levels, even the 2 layers of parallaxing background!
Also you can import your custom made characters!

Gameplay
You can walljump, wallclimb with a pickaxe, and doublejump to quickly move around.
Shotgun ammo & grenades are infinite, battles are quickly won by those who master the easy controls.
Grenades can be cooked (hold button = grenade timer).
If you have kills and you do a grenade suicide, a kill is substracted in the form of a large golden jewel.
This jewel is thrown into the level and can be taken by any player giving them the kill you worked for!
So cook those grenades :-)
The gametypes are deathmatch and last man standing.

Controls
Requires a gamepad or a arcade/fightstick to play

Extra info
I have made this game so, that you can easy access your game files.
This makes it possible for you to pack your levels/backgrounds/characters into a zip and send it to friends any way you like.

A special thanks to everyone who voted!