Nicely done! Some minor suggestions to make it even nicer:

• add a grace jump/coyote jump/ledge forgiveness mechanic (different names for the same thing). This means that when there is a platforming section, you get a few frames of "grace" when walking off a platform to actually perform the jump, making platforming less frustrating. I constantly accidentally ran off platforms before jumping on the way to the "second" emblem haha
• consider adding a boss health bar. This is more of my own personal preference and not a "must", and many games thrive on not showing this kind of information to keep the player guessing, but I personally would have enjoyed the fight more by knowing how well I am doing (my own health loss vs the boss's health loss), and how close I was to beating the boss on my failed attempts.
• on the way to the boss, one of the chambers (4th one if you take the fastest route) requires you to wait for the flames to disappear before you can proceed. While good for teaching the player how the flames work (and in general, the dungeon is nicely built to teach the player the mechanics and enemy types without a tutorial), it stops the flow when you have to rerun from the beginning back to the boss and you need to idly wait to proceed without losing health. No other chamber requires that at that point, and it's only like two seconds, but if you die constantly like I did, it'd be nicer to just keep the flow going.
• transition from the chamber with two arrows and all the blocks that need to be moved out of the way, back to the previous chamber puts you immediately next to a snake enemy, making avoiding getting hit extremely difficult, I think this is a slight oversight.
• consider making the invulnerability window after getting damaged slightly longer, as it's easy to get thrown off the flow and damaged a few times in a row as it is now.

But these are just some suggestion, it was a cool experience reminding me of old DOS games, and congrats on the work!