[PC Windows][early 2000s] 2D side-on party shooter arena, local multiplayer

Platform(s): PC (Windows)

Genre: 2D side-on, platformer, party shooter arena, local multiplayer (up to 4 players)

Estimated year of release: Early to mid 2000s

Graphics/art style: 2D, cartoony, modern setting, pixel-art (don't remember how detailed, but I think it was not too pixely).

Notable characters: Four human players with basic character editor (memory fuzzy on that, it could have been four characters with preset colors, but I think you could at least choose their headgear/outfit). You could change their name from Player 1 - Player 4.

Notable gameplay mechanics: Map editor, several map choices, the levels were generally pretty vertical, maps included a city with buildings, a lab, sewers, a nuclear plant, and I think a castle and some wintery and island themed levels (not so sure on the latter three).

Each games lasts a few rounds, you spawn in a medium-sized arena with basic guns, you earn money in the 100s each round (and on kills) that let you buy better guns. There was loot randomly spawning around the map that gave you health, armor, and guns I think ? The weapons went from a handgun, to a SMG, a shotgun, and a rocket launcher. You could shoot through windows. Some levels had radioactive waste that could hurt you.

Other details: The game was indie, you could download it for free on the developer's website, it had an installer, it had a sequel eventually (I don't think the first one included the level editor yet). You could play up to four players locally with specific key bindings for each players.