Zion of Olympus Have you though about adding weaker/basic versions of succubuses as mobs to roam/patroll the map? It might be a little extra work but it would make navigating the map better,the plant monsters now are just torture,to see how much sanity you can lose by the time you get to the boss.
Second point would be if you can make battle bigger,to clarify i would (and not just me) for bosses to have backup in form of weaker succubuses which makes sense since generals and such wouldn't fight alone especially against a rampaging hunter of their kind,maybe even mob battles to feature more than 1 in a fight.
To balance this you could have the protag hire allies/mercenaries,companions to help him till he reaches the succubus boss,where he fights alone (an explanation would be maybe they are holding the succubuses on the other side)