Beating the final boss aka floor 9 is not too hard if you go for the right build, key sword is not a good build btw. If you get whetstone try getting all the shivs, put it in the corner and line both below and to the side with shivs, spend your energy on stone and see big numbers go brrr. Easy build since all ingridients are obtainable. Its the more obscure and shenanigan dependant runs that are hard to get but let you go deep into infinity runs))
my biggest problem i've faced with the game has simply been my luck with finding items. the build sounds fun and possible .... if i actually got even some of the more useful common items on a regular basis. in that run alone i saw only the lucky shiv, one cursed shiv, and two normal shivs with one of them popping up in a late run shop.
(should add : this isnt a problem with the game. [it's a rouge like. i expect this] i just have horrid luck for getting even the basics of items when it comes to RNG sometimes. and i am VERY excited for what the devs behind it end up making with it in the future.)