Hey Michael!
Overall, the boss feels responsive and has some challenge to it, which I enjoyed.
I think it is a little easy to defeat because of the player having the double jump and dash abilities. I think this fight would benefit from moving the one-way platforms down so the player has to jump to those to jump over the ground slam waves. Since the dash can be activated as soon as the state ends, it is easy to get behind the boss, slash, then repeat. Also, the dash makes the slam waves feel like there is minimal urgency to get out of the way.
For the boss' moveset, attacks seem fair with the way they telegraph. I especially like the dash attack the boss does. Doesn't seem too fast or too slow, I can tell it's coming and that I better move out of the way. I think damage for all of the attacks feels balanced. Maybe if the player had more health, damage would need to be tuned up a bit.
The slam phase is great as is, if I could offer an idea it would be that the boss could do the slam in three different positions in the arena. It could be cool if it cycled through those one after another, so it puts some pressure on the player to know, "hey, I need to be at this platform to dodge this wave, but I'm on the other side, so I better move now!" Maybe the boss could have a cooldown period where it rests for a second so the player can get some good damage in and have some time to breath before getting right back into it. A larger arena might be better for this though.
I do believe this boss would be memorable. I'm trying to picture this fitting into a full game and like any metroidvania game I've played over again I think I would have that moment in a new playthrough where I think, "Oh yeah, that boss is coming up soon and that was a fun fight!"