Bypass any OTP: you only need email:pass to access an account. Simple as logging in to your personal account
No kick on password/email change: if owner changes password or email, you do not get kicked out of the account. You remain logged in despite password/email change. Neat.
Owner can't log your device out: the owner has no way or power to kick you out of the account at this point, not by changing emails, passwords, or even removing you from the allowed device list. you have more power than the owner.
So as soon as you log in to the owner's account, they cannot get rid of you. You are to do to your heart's content.
Obviously method is private and no one knows it but me, unless somebody else have found this.