Haii heres an (updated) guide for all the bosses v0.4c
Slime Queen - I don't have *great* advice for her persay since I mainly brute forced her since I couldn't figure it out, but I know you're *supposed* to reflect her gun projectiles with your magic and whatnot, I just never got the hang of it. Instead, I kinda just dashed behind her a lot and went ham. For her second phase, I essentially just did a high jump whenever she teleports. And I mean HIGH because if you don't go high enough she will catch you with her melee attack! Otherwise I did the same stuff, just get the jump timing right and brute force like before
Oni - She definitely feels more forgiving this time. I had to get over my Oni PTSD and found out that she's not unfair anymore! The plan is simple: She will jump to EXACTLY where you were, meaning that if you move slightly out of the way and swing early, you can stagger her very easily. Easy win yay good boss now!!!!!
Milly - This is one of the first ones where I explicitly recommend a weapon/spell. In this case, I recommend using heavy weapons that you can buy from the shop, like the Axe or Mace or whatever they're called. They do HUGE damage. Why? See, in the fight, you're essentially dodging all over the place and punishing her with a dash cancel attack (aka dash and cancel the momentum midway with an attack, being to avoid her attack but also be in range to counterattack quickly). This is especially powerful when you use said heavy weapon's special skill (consumes all of your stamina) to almost guarantee a stagger and do a bunch of damage. Also she's like mega predictable and you'll be dashing constantly to avoid her two attacks (especially her 3 lightning bolts). FYI when she exits stagger she will strike lightning around her.
Shadow - Weapons don't work like at all against this guy so it's all spells babyyyy. Use the ones that do a bunch of damage like lightning or ice, i dont really use fire for this one. Your weapon doesn't really matter since all they're used for is to recover mana (maybe use the one with the highest MP restore idk). The gameplay is super simple: When you see the super obvious attack, dash behind him, and use your spell/weapon to counterattack. Avoid the black puddle residue at all costs. Staggering him is bad and kinda inconvenient since it summons black puddles going your way from the edge of the stage going towards you. You can either not stagger him and take the patient route letting it restore by not attacking him, or be a chad and jump over it. BTW from what I've seen the black puddle is essentially a run ender since there's no way you're recovering without him putting you *back* into big mode.
Swamp Witch - Easiest cheese in the world. Equip the Slime Daggers and use its special ability on her fireballs lmao.
Like seriously, the lingering hitbox lasts so long it reflects the fireballs so well she dies so quickly its so cray cray i can't make this shit up.