Joffrey has immune to triggered effects. So does this mean he cannot use a duplicate to save himself. Using a dup is a response, a response is a triggered effect so I am thinking that he can't but want to be sure.

(4.2) Duplicates

Using a duplicate to save a character is considered to be a gained triggered "Response:" action. Thus, it is treated as a triggered effect and may be canceled, but because it is gained (and therefore an ability of the card attempting to use the response), a character who is "immune to triggered effects" can be saved by using a duplicate, as a card cannot be immune to its own abilities.