Presumably 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 and Evil Leafy (who was already outside of the TLC), would later become contestants in Battle for BFDI.
Amor Boretto announced on Twitter and the BFDI Patreon that if jacknjellify gets $1,000 pledged monthly, a debut will happen. On October 1st, 2019, the goal was met and the debut was confirmed.
In "The Escape from Four", a group of assorted recommended characters pestered Two into hosting a debut, to which they buckled. 26 recommended characters were up for voting, and the winner would join TPOT.