Debut

A debut is when a brand new contestant joins the show that was made by a fan/viewer of the show. Every season has at least had a debut planned at one point.

BFDI
In The Reveal, it was announced that one of 30 recommended characters will join Battle for Dream Island. In Reveal Novum, David won.

BFDIA
Apparently, the winner of BAGUETTE was going to choose a character to join BFDIA. Due to BAGUETTE and Battle for Dream Island Again's cancellations, this never happened.

IDFB
Persumably every episode, viewers could pick out a character to join the BFDIA remnants. Most of these were brand new characters who never joined BFDIA or IDFB. All of them, save for Nonexisty, would later become contestants in Battle for BFDI.

BFB
Amor Boretto announced on Twitter and the BFDI Pateron that if Jacknjellify gets 1,00$ pledged montly, a debut will happen.