Cool concept! I like the idea of switching between two characters to co-op with yourself to stay alive! The lighting looks really good and you managed to make a flat 2d game have plenty of depth. A few comments:
- A cooldown timer on the weapons
- Animations for the sword/staff
- More effects/particles on enemy death
- Maybe item drops/hearts when killing enemies
Overall it seems like you achieved a lot in the 48h to make this. I think another few hours of polishing and you'd have a great little survival game. Really good job!