Source Engine third-person beat 'em up platformer mod Thread

Introduction

I've been thinking about creating a third-person, bird's-eye, beat 'em up, platformer mod using Source Engine.

Features

• Full 360 degree movement
• 4-player local co-op
• Multiple playable characters
• Switching nearby characters in story mode
• Replayable levels
• Free Play mode with the ability to switch characters on the fly
• In-game achievements
• Bonus levels
• In-game & FMV cutscenes
• Power-ups
• Upgrades
• Skins
• Art gallery
• In-game cheats
• Other extras

Controls

• Move: WASD, Left Stick
• Jump: Space, A Button
• Attack: Left Mouse Button, X Button
• Special: Right Mouse Button, B Button
• Interact: E, Y Button
• Previous Special: Mouse Wheel Up, LB
• Next Special: Mouse Wheel Down, RB
• Switch Nearby Character: F, LT
• Block/Crouch/Roll: LCtrl, RT
• Character Select (Free Play): Q, D-Pad Up
• Previous Character (Free Play): Z, D-Pad Left
• Next Character (Free Play): X, D-Pad Right
• Toggle HUD: Tab, Back
• Pause: Esc, Start

Conclusion

Is it possible to create it as a Source mod, or do I have to edit the engine's source code?

Edited by: Gorilli09