So I made the mistake once of allowing Invisibility to work on two creatures when one of them is carrying the other. One of my players is insistent that a creature climbing onto another creature counts as being carried, in spite of me deciding to never let that happen again.
He then asked the following question as a basis for his argument:
If a person is wearing a Cloaker as a cloak and they become Invisible per the Invisibility spell, does the Cloaker not become invisible too?
Seeing how that is actually a more legitimate example of one creature actually being "worn or carried" I am not sure how that works. I am willing to ignore how it was ruled before, as I am partly asking for future campaigns where there is not a history of the players doing it.