This is Mr. Nostalgia's True Form after his trip through the TV Zone, where he was sent there by his own brother, Mr. Puzzles after he tried to put a stop to whatever Mr. Puzzles is planning to do to get that 5-Star Rating that ended up with him turning into a glitched out amalgamation until he was given a body by the TV men to  take over as a vessel.

Now he has vowed revenge against his own brother for what he did that made him turn into the monster he is today.

He is also the reason that he gave Y/n aka SMG5 his Fatal Error Form aka Fatal Error SMG5 after the Mar10 Day Fiasco when SMG4 became obsessed over making the perfect video.