Its one of the most dangerous bosses around. But it can be easy to handle. You'd want to flash both Honeygast and Mitsuro at the same time to prevent them both from targeting you at the same time. Flashing the Honeygast also prevents him from constantly spawning the Waboomi to overwhelm you. If they do spawn, take them down immediately before then returning your gaze at the bosses. After Mitsuro is taken care of, the boss will begin to spawn flowers and Spookobolds. If the later spawns then let go of the Honeygast and deal with the Spookobolds first. As for the former, the Honeygast will try to pull you into the flowers to sun you as you're siphoning them. Let them go if you get to close to the flowers. Repeat all of this, avoid the honey, prevent the enemies from overwhelming you in numbers. And you'll eventually win soon enough
Though one thing I have noticed during the playroom is that if you let Honeygast eat you and not struggle for a bit. The heart that would allow you to befriend ghost and add them to the "Fed" part of the ghostiary appears after long enough. Though Idk if that would count with the Honeygast. Same happened with Mitsuro (I presume the same is Mirrim though Idk if she or Mituro can be eaten)
Mirrim can be found in the Observatory, Funhouse and the Dilapidated Halls. Though in both she has a 1 in 256 chance to spawn. So be ready to face her. Idk if she can be fed or eaten though since she's the only one I can't play with in the Ghostiary yet despite eating and feeding every other ghost there