Hello. It's the same as all other bosses. Check out their attacks and find a way to counter them. For example, slime's fireballs have an audio cue before appearing and can be blocked without losing any HP if you will face in the right direction. On the other hand, its jump attack can only be avoided by running out of the way, so save a bit of stamina.
It's the same deal. Check out the attacks and figure out a way to block or evade them. Sort of like a mini puzzle in the real-time mode. Or just facetank some damage and deplete their HP faster than they drain yours. It's a playstyle thing too.
Glad to hear that the improvements are noticeable. I look into all reports from players about weird behavior and potential bugs. If you'll encounter anything strange - send me a message with details and I'll check it out.