It's fun so far. The theme is funny. Please expand it to deeper Fromsoft lore too. Scrolling serves as a nice twist to the game.
The difficulty curve is shaped like a staircase, which is no good. You spend a lot of time doing nothing and then it ramps up quickly and back again.
Many of the upgrades feel like junk.
There is a clearly dominant strategy in herding everything at the middle-top section of the screen for collecting at the bottom and then picking off threats.
It is not even worth continuing if you don't roll the staff at the start. The staff is way too good already on its own, but having so many walls of rats that it is uniquely positioned to farm gives runs that get it early way too many gems. Most of the threats later on are frail glass cannon enemies that appear in awkward places, failing to give any other weapon an advantage. The creatures that look like actual bosses and have the HP of one barely do anything. They quickly dispose of themselves by lurking around the AoE. The way these layouts are designed currently rewards mobility and range consistently over melee and dps output, so upgrades that concern the latter aren't very good.
I like how RTSR is just as OP as the one in Dark Souls.
The way you have to go to the shop manually at the moment is cumbersome and doesn't seem to add any depth. Maybe each additional time you level up before shopping could get you a reroll? Also, you should have that bar be better positioned, such as by putting it right below the character, because it's annoying to look away to find it during normal gameplay.
The playable character needs more contrast. I should be able to tell where I am while I look elsewhere to aim.
Right clicking to open the shop would be a better solution than moving the cursor over to the other side of the screen, too.
There are optimization issues and they disproportionally stem from the lighting skill. Consider simplifying the visuals for that
I got to 20 million and thought that was a good place to stop. Surely that must be enough avenging for Zanzibart to forgive me.