I have found the over powered strategy!
Summons are honestly super op, esp with 5 mana cost cementary that you can loot from lich. Skeletons are also super great.
How the strat works:
Pick creed of impulse, you will need the mana regen and won't be aiming at the end. Any boss that spawns extra enemies you take a card, otherwise take an artifact. Take mana artifacts (most summons cost 3+), and mostly filler is fine.
If you see gravekeeper don't loot a card, loot for artifact. He has a reasonable drop chance for a spade (it might even be guaranteed if you don't have it), and space gives u +3 dmg with little boss empowering.
Good bosses to loot:
Keeper of Cantharus: He has a laser summon! free dmg
Mucelian Patriach: Has a blight spawn that is good for tanking
Ash dude (forgor his name): He has a wizard summon who shoots fireballs.
Melee Bosses really like going after your summons, which means they stop being so much of a problem! You can kinda just sit back and just dodge the aoe weaponry after you start spawning in your army.
Ranged bosses just get overwhelmed and brutally slaughtered.
Basically built my own raid force by taking only summons.
I would've gone further if I had more time (died intentionally just to get to the end screen). Will send an update of how far I can get.
Very fun, butcher op pls nerf
Game got a lot easier after getting a couple of artifacts (namely damage). Got a couple of flat dmg artifacts, the prism artifact (+4 dmg super op) and a +30% dmg artifact.
I then swapped all my skills to either 0 cost dashing skills, or beam skills (cuz of artifact). This allowed for pretty easy kills, as I could dodge a bit more with the extra dashes from moves but unfort got beaten by the butcher who just jumped me so much my stamina ran out and my dash attacks weren't large enough to evade. (the run was done on creed of impulse for more mana regen to spam)
Suggestions:
It would be nice to try and make how artifacts work explained a bit more, I don't quite know what "duration" is, nor how increasing boss damage would do anything (as each hit only takes 1 heart). A more in depth explanation of all these abilities and what they do would be nice!
It did somewhat bother me that you always had to swap something after winning, but I realized that the theme of the game is kleptomancy and it would be dumb for me to suggest allowing you to skip.
Difficulty:
It gets much easier to kill the bosses once you have damage, so much so that the first 1-3 bosses are more likely to kill me than any other boss. Would be nice to have bosses nerfed, but have much stronger powerspikes as you grow, to keep the challenge.
Minion hp: Some feel immortal (they might be I have no idea), some end up cluttering the screen to the point where you can't walk (little green blob mine things).
Overall great game! It was very fun, albeit extremely challenging. 
LMAO found a glitch. Destroyer (the cannon boss) can't kill urso if urso has the shakeoff ability, urso simply stays at 25 hp (takes death worthy dmg and heals back to 25) its gotten me stuck in a loop bc destroyer is perma stunning but i can't die so i'll be here for a while until my urso has some massive stats
would've been able to kill the final boss if i had put some damage on him... was nigh unkillable tho