The first boss in Rogue Legacy 2 is behind a door. You won’t be able to encounter them until you finish a few things in the castle, and you can bet that it will take you a few generations to make it through to the end. The two things you need to do before worrying about the boss entrance is gaining the dash ability, and the inner demon abilities, which allows you to read the glowing blue locations in the castle.
You can find the dash ability and the inner demons ability hidden throughout the castle. There’s no set way to locate these rooms because each castle layout is different for every character you play through. For the dash ability, you want the statue of the Ananke of the Shawl. Then you have complete the challenge associated with that statue. For the inner demons ability, it’s the Power of Empathy trial. Both trials feature the same challenge and route every time.
Once you complete those, you can unlock the first boss door. There’s no set location for this room, so it could take you a few runs to find it. The front entrance should have two lanterns with red crystals inside them in front of the door. You have to activate these lanterns shortly after the other. The only way to turn them on at the same time is to jump on one, do a spinkick, dash to the other, and then spinkick it to activate. It can take a few times.
After you successfully hit the second before the first lantern goes out, the door opens for you to face your first test.