You battle the "final boss", the Binary Bard (Mordred) in a robot warrior suit. It has spinning sword arms, fires homing projectiles, and drops bombs on the floor. You fight him as Merlin the owl, and then as your knight. (see related question)
you have to finish the puzzle then click on the door
there is a code you can get from somebody!
you do the puzzle
No
You go through the puzzle door and beat Mordred. (see two related questions)
Into the castle. To follow him, you have to solve the puzzle door. (see the related question)
the door that's locked
Solve the door puzzle and battle Mordred to save the (real) Princess. (see related questions)
go to the secret door
Solve the door puzzle (he's Mordred) and battle his robot warrior suit. (see related questions)
In the palace the right door
You can click on the door behind "her", but if you give her the weapons, you have to solve the door puzzle to enter the final battle against Mordred. (see the related question for the solution)