Nonexisty

Nonexisty Nonexisty is one of the 30 recommended characters that could've joined the game in episodes 17 and 18. He placed 8th with 11 votes. He was also up for voting to join the second season, but he only got 266 votes. Even if he had gotten enough, he still would be disqualified for being absent, and was the only character not in the original BFDI cast to be disqualified.

He was one of the two contestants not participating in Battle for BFDI.

He apparently busted Nickel out of the LOL, to join Inanimate Insanity I, in which he also spoke.

Nickel
In an episode of Inanimate Insanity, Nonexisty was the reason why Nickel escaped the Locker of Losers.

Ruby
In Reveal Novum, it's revealed that Ruby can see Nonexisty, as she points out the Sender Scoop Thrower missed him.

Trivia

 * Nonexisty apparently tastes of peanut butter. He made a cameo in A Leg Up in the Race, after the Announcer stated that all previous votes would be deducted from each contestant's score. Firey noticed that he tasted peanut butter, and an annotation appeared with the fan character credit.
 * Nonexisty was the second recommended character on the show, as Bomby was the first in Lofty.
 * Nonexisty is one of the three characters held in the TLC to not change his design in IDFB, with the other two being Grassy and Firey Jr..
 * Nonexisty made a cameo in Inanimate Insanity and said his first and, so far, his only words: "No Problem".
 * Nonexisty is the only character on the show to be 100% transparent.
 * Nonexisty and Evil Leafy are the only characters that appeared in IDFB who did not compete in Battle for BFDI.
 * He is the only major recommended character that never became a contestant.
 * Possibly, he's holding Bell's string.
 * But that might also not be the case, because he might not be able to hold anything.
 * Nonexisty was never eliminated in Reveal Novum, because the Sender Scoop Thrower missed him.