There is a glitch where the player is invicible after mashing UP (or Button1 with jetpack) when going through a door.

I can look more into detail but from what I undersand by looking at the assembly code and the ram:

• When entering a door, the game set the player invicible flag (0x0308 to $20). I'm guessing the game does that to avoid getting hit while transitioning to the other room
• When the player transitions to the other room, the game will revert the invicible flag (0x0308 to $00)
• When UP (or Button1) is press 1 frame before the game revert the flag, the code for "set door transition invicibility" will be called again after the "revert invicibility" code. I'm guessing the game still allow you to entering the door again as you haven't transitioned yet.
• Doesn't work if the player is already have iframes, the countdown will still be active and it will turn off the flag after some times

Yes, it's frame perfect! it's 5 or 6 frames after the first button press.

The best way so far is to smash and hoping for the best. There are no visual indication if the invicibility is on, the only way to know is to try getting hit by an enemy.

Pause buffering doesn't seem to work. If it's possible, it would be a great consistent way to get the glitch

did a video to explain some details