using chaos orb to get some pretty damn high xp boost upgrades and a upgrade that can attack everything makes it op.
you'll be able to hit pretty much everything at once, and rats always have 1 hp.
a kill also raises your multiplier if i recall
then the fact that you can have all your upgrades relate to black tiles.
also
i found out that the way tiles generate is usually in a way that ONE match is always possible, but getting black tiles to spawn naturally via the ¨twice as likely to spawn¨ upgrade, this seems to break.
Right right, so it does need "a bit" more of setup besides just being OP on its own. And the tile generation is absolutely random. Reaper just adds a 10% chance of getting a black tile too (so still lower than the normal colors). Unless of course if you stack it with black Trump card in which case it is bumped to 30%.
