Metal Arms: Glitch in the System/The Zombiebot King

Any% Easy Route

Use Scatter Blaster for first hit (Throw or use slingshot for coring charge depending on your preference)
Pick up Rivet gun by the furthest wall
Use combinations of rivet and scatter ammo of needed.
It is typically a good idea to open the grate with the mega energy during or after the 3rd hit

This boss takes 5 hits from coring charges to take down.
It takes the boss 3 seconds to recover from a coring charge hit
Rocket Launcher ammo is behind your spawn. SPEW, Rivet, and Scatterblaster ammo are along the far wall.
The first grate on your left contains a Fleet Foot booster, which makes this boss a lot easier to manage.
All Items on this map will respawn (Health takes longer to respawn)
Using Scatter Blaster on small Zombiebots is recommended
Using Rivet Gun on the King is Recommended
One Zombiebot comes out after the 3rd hit
Two more Zombiebots come out after the 4th hit
After defeating the boss, Mozer gives you the level 2 rivet gun.