The New Mechanical Boss fights are great, and seem to currently be the best decks in the game which makes sense for their place in progression. I think only the queen bee sticks out as a little under powered.

King Slime's fight feels a little too strong when rng is in his favor, stronger deck than EoC in general

King Slime drawing 2 mother slimes on turn 1 and possibly having 6 slimes on turn 2 including himself is basically unbeatable(at that stage of the game i believe, due to 8 damage + 1 heal to all for 4 mana (mother slime will have 8 atk for 3 mana after king slime buff) unless king slime is supposed to be a fight after all the possible npcs post EoC

The only time I managed to beat him (running cavern equipment w/ mimic pack cards) is due to ai misplay putting mother slime onto the defense slots, king slime deck should probably only contain 1 mother slime and maybe just one pinky too, otherwise just tough, cool fight where you have to pick your targets because thorns limits the possible targets with the high, consistent damage of pinky + jungle slime attacks keeping you checked, or the mother slime in the worst of the worst scenarios becomes a one shot machine that cannot be stopped once your board dies