OS Graveyard is the fourth stage of IT Catacombs, a straightforward boss after boss battle. Requires proper meatshielding to win.
- Professor A. appears after 2 frames.
- Bun Bun Black appears after 26.7 seconds800f
- Teacher Bun Bun appears after 33.3 seconds1000f
- Because this stage only ever spawns 2 enemies at most, Teacher Bun Bun won't always appear at the time stamp, but he appears when either Professor A. or Bun Bun Black is defeated.
Uber-less line up
- Mohawk, Manic Mohawk, Eraser, Manic Eraser, Prisoner, Crazed Bahamut and Dark Emperor Catdam.
- Demonstrated Video: 
Max up power up. Use meatshields to stall until you have enough to spawn Megaphrodite. Stall black Bunbun with Bombercat and meatshields till Megaphrodite kills Prof A. Have Necrodancer and any other cats which freeze flying enemies. Use Windy or A. Bahamut to finish.