How do I fix stutters in Dead Cells?

One unlikely solution to stuttering and freezes is to disable internet connection. I can't explain it, but it worked for me wonders. Go to Control Panel > Network and Internet > Network Connections or type view network connections into the Start input panel, and disable your internet adapter by right-clicking. After playing, re-enable it to be able to use internet again. For some reason a custom Windows Firewall rule to block the game exe didn't work for me. Obviously, this solution might not be needed in the future, as the developers are still working on the game, but for now that's what works.

The major thing that fixed it for me was just putting it into Windowed Mode. I was able to run the game flawlessly on my comically weak Surface Pro 4 with an M3 processor by just switching out of Full Screen mode.

They also fixed some of the lag when they recently released the full game, so this isn't as much of a problem now anyways.

I suggest updating drivers for your gfx card. If you are using Radeon Crimson drivers then go to the game options menu, hit "Dead Cells", and disable morphologic filtering, enamble vsync and 3 buffering in OpenGL, and decrease tesselation to levels like x4.