The out of bounds route is pretty simple, but it can only be performed on a fresh save file, since it involves the first tutorial. You'll need your sound on since you won't be able to see yourself for some of this. Turning you music volume down is recommended but not required. There are two slightly different versions, with one technically being faster but with one part of OoB movement being a bit harder (and waste a little bit of time if you hit the loading zone), and the other wastes a very small amount of time for easier and more consistent OoB movement to help you avoid hitting a loading zone and wasting time.

Here's the first one without the easier OoB:

1. Reach the first battle tutorial.
2. Continue through the tutorial until the part where you need to crouch to dodge an attack.
3. Dodge the attack by crouching, but right after you do, jump before more of Elizabith's dialogue starts. The closer to the dialogue appearing when you jump, the faster the jump will be. Careful tho! Jump too early and you can actually fall into the ground or (hilariously) levitate above the ground. You can perform the glitch correctly so long as you float up, but the slower you do, the longer you will have to wait.
4. You should now fly off into the sky like you're name is Buzz Lightyear.
5. Advance through all the dialogue, but stop at the last line of dialogue, "Defeat that monster!" The faster you floated up, the less time you have to make sure you're ready to dismiss the dialogue box right away.
6. Wait until you have escaped the battle. The battle screen on the left will disappear, and the monster will resume wandering around.
7. Advance through the final line of dialogue. If you dismiss the dialogue box before you have escaped the battle, you will be forced back down on the ground.
8. Immediately start gliding to the left. If done right, you should land on the rocks above the loading zone, but still be failing instead of properly landing.
9. Once you are on top of the rocks, let go of your glide, but keep going left.
10. As you keep holding left, you will go off screen, and fall off the rocks to below ground level (as indicated by the camera moving down), and then eventually be teleported (as indicated by the camera rapidly moving very far up and a bit to the right).
11. Once you zip, start gliding to the left again.
12. Listen to the game music carefully, and wait for the gliding sound effect to stop.
13. Once the gliding sound effect has stopped, you will now be in a "swimming in air" state.
14. Now start swimming up and right.
15. Once you see spikes, just keep going right, and be careful not to touch the spikes. Their hit boxes extend farther down then they appear!
16. Once you reach the end of the spikes, go up the right of the wall until you are above it.
17. Once above the wall, go to the left until you are above the loading zone from the boss key to the area where the boss door is.
18. This is the tricky part. You'll have to swim around until you either fall through the hole and back into the level, or touch the loading zone and have the game fade to black. Make sure to go back if you touch the loading zone.
19. Once you are in bounds again, jump over to the chest and grab the boss key.
20. From here, just go back into the loading zone, and go right to the boss. Happy boss fight!

Here's the second one with the easier OoB:

1. Reach the first battle tutorial, but before entering it, wait for it to walk to the right. Stand near it without starting the fight, and pause the game. The aminoguana will walk into you and start the tutorial (and letting you regain full control of yourself) while the game is paused. Be sure to move your pause menu cursor over controls so you can press enter to advance text without dismissing the pause menu.
2. Continue through the tutorial until the part where you need to crouch to dodge an attack.
3. Dodge the attack by crouching, but right after you do, jump before more of Elizabith's dialogue starts. The closer to the dialogue appearing when you jump, the faster the jump will be. Careful tho! Jump too early and you can actually fall into the ground or (hilariously) levitate above the ground. You can perform the glitch correctly so long as you float up, but the slower you do, the longer you will have to wait.
4. You should now fly off into the sky like you're name is Buzz Lightyear.
5. Advance through all the dialogue, but stop at the last line of dialogue, "Defeat that monster!" The faster you floated up, the less time you have to make sure you're ready to dismiss the dialogue box right away.
6. Wait until you have escaped the battle. The battle screen on the left will disappear, and the monster will resume wandering around.
7. Advance through the final line of dialogue. If you dismiss the dialogue box before you have escaped the battle, you will be forced back down on the ground.
8. Immediately start gliding to the left. If done right, you should land on the rocks above the loading zone, but still be failing instead of properly landing. You are now free to dismiss the pause menu, or "unpause" the game. The camera will now always follow you even when going out of bounds where it normally wouldn't follow you until the next time you touch a loading zone. This will make lining yourself up to fall down a hole without touching the loading zone later in the guide much easier.
9. Once you are on top of the rocks, let go of your glide, but keep going left.
10. As you keep holding left, you will fall off the rocks to below ground level, and then eventually be teleported (as indicated by the camera rapidly moving very far up and a bit to the right).
11. Once you zip, start gliding to the left again.
12. Listen to the game music carefully, and wait for the gliding sound effect to stop.
13. Once the gliding sound effect has stopped, you will now be in a "swimming in air" state.
14. Now start swimming up and right.
15. Once you see spikes, just keep going right, and be careful not to touch the spikes. Their hit boxes extend farther down then they appear!
16. Once you reach the end of the spikes, go up the right of the wall until you are above it.
17. Once above the wall, go to the left until you are above the loading zone from the boss key to the area where the boss door is.
18. This is the tricky part. You'll have to swim around until you either fall through the hole and back into the level, or touch the loading zone and have the game fade to black. Make sure to go back if you touch the loading zone.
19. Once you are in bounds again, jump over to the chest and grab the boss key.
20. From here, just go back into the loading zone, and go right to the boss. Happy boss fight!