Please report any bugs you encounter here
Deleting all the blocks in a piece then swapping can cause blocks to spawn inside other blocks. Also had a bunch of widener perks in case that matters.
Screenshot is just to show off my build. All 10 gold 10x1's at level -14 so blocks were basically stationary. Eventually I accidentally double dropped on the start column but it would have been easy to go forever if I didn't get impatient. Being able to lower the level indefinitely is probably too strong and not that fun once the novelty wares off.
That bug should be fixed now, thanks for reporting it!
I also made a change to the shop that will make it harder to reach extreme negative levels, still considering other ways to make those levels more interesting. And the rate at which drop speed changes probably needs some tweaking.
Also, nice build! Now try for all 10x10s