The depth of combat might be improved via introducing mix-ups. combos and more-or-less expanding queen's painfully narrow arsenal. Which would solve two problems - hero having a designated answer to each separate move of the boss and the part where the opponent just dances close enough to the model so the hits, no matter which phase, basic attacks cannot reach him and slow specials are effortlessly dodged. So, how it would be able to do it while saving the three-button + WASD controls? Well... in a current state, each button - strike, dash, area for short is going off with a delay before and after, which allows the opponent to avoid and retaliate effortlessly. But what if there would be more than one move in a chain, for example - up to three? And the shape in which this move will be executed would be dependant on which action was performed prior, including the same one. If we model a situation, it would be... for example - in the first phase, you make a dash, the hero jumps or outspaces. But, the follow-ups couls be a spin-attack with a mace that moves forward, or a soaring motion, as if the queen does a run-up to a jump of her own, culminating in a circle of dark energy, which can be followed up with a dash in a different direction a slam-down with a minor shockwave, or the circle at the feet of the hero, similar how area works now. And only after that, there is a recovery window for the player's attack. That'll make the queen feel truly powerful, as she should as the final boss. Such potential might be unlocked with progress as well. And, to help realise the second phase in such a manner, the healthbar on the transition would better fill up, as with the upgraded sword, it gets over way too quickly, and would rob of the excitement to play with her moveset one it gets hotter. It would be also a prime opportunity to fix the blind zone the second phase has.
Such a system would require a timer, in which an attack could be followed up. If it doesn't - the recovery ensues. The final part of a combo having a longer recovery time would fix the potential problem of button-mashing.
In general, such an expansion would make "The Dark Queen of Morthholme" feel like a much more engaging fighting game.
Not to mention, leading into a more intricate deconstruction of tactics and martial prowess in the exchanges between main characters, akib to the one you have if you keep beating the hero up with just the mace.