I know it's not lesser known at all, but it might have gone under your rader because you might not suspect it.
Did you ever try Kingdom Hearts games in critical mode? Especially 2 and 3, they are fantastic action games with a big challenge, and some of my favorite boss fights in gaming. I'm really putting an attention on "critial mode", because it's what changes everything. It's not just an higher difficulty, it totally rebalance the game for a different experience. It's harder but you also have access to more skills etc, making it one of the best action games in my opinion.
It might not seem like it in this no damage video, but this is maybe the hardest boss fight I ever played, took me about 10 hours to beat. It has very tight timing and you need to learn a lot about your oponent openings etc. I love the boss in this series, very interesting duels.
Now for something more like you asked, lesser known and in the janky-ish territory, I'd maybe suggest this one:
It has that eurojank vibe, but if you can go past it, it has some pretty cool gameplay systems. There are different combos and weapons, but you can also rewind time, and when you rewind time, your previous version of you will still act what you did before rewinding time. Let's say you are against a big ennemy, you can start shooting at him from on corner of the room, then rewind time for 10 seconds, and during these 10 seconds, you can go fight this ennemy while your clone is shooting at it, and you can rewind again and now there will be both your clone, shooting and melee fighting, there with you. It's like creating temporary allies and doing various situations with them, it can be pretty satisfying and fun. It's not an amazing game or anything, it feels cheap, but it's still fun enough and fits your criterias I think.