Am I missing the dungeon cores somewhere in the boss room or are they just not in the game yet?
gotta perfect the dungeon. no downs, if you need help with that talk with the npc's they can give stat ups for gems... the one in front of the wagon whos rude is actually REALLY helpful. from there find a weapon that suits your playstyle.
bows are junk in my opinon because you cant see where your aiming.
staves are a nice option for range, but the homing can screw you over because it takes the direct path to the nearst target... dosnt path around objects a blessing in disguse against foes, they also can combo.
shortswords are fast but weak, good for counter attacking because they are also light on stamana
axes and longswords hit like a truck but also drain the stamana bar like nothing else. these are what i use, when used correctly they can kill your foes fast.
some other tips
pay attention to item effects. some will tip odds in your favor drasticly, some only really work once you get a matching pair or set.
sometimes hitting esc and forfiting is the right call, you get gems per floor regardless of performence. if your struggling dont be affraid to run till you get stronger. you get to keep the gems thankfully, and the items use this to come back stronger. nice mercy mechanic i think.
rescues make great bait for strong foes, got a cheap lifesteal boss? keep reviving your allies. lifesteal cant take more life then you got.
you'll know you got a core cus it looks like a gobstopper and its visable ON the chest.