Mystery Teaser Closes NXT, WWE TV Hacked?! (WWE News)
Mysterious image appears at the end of WWE NXT. Who's coming to Vengeance Day?

WWE NXT teased a new...something at the close of Wednesday's show with the apparent hacking of the feed to display a TV test card displaying "Vengeance Day" where "WWE Transmission" had been before.
The show immediately went off the air, leading to the safe assumption that the mystery will be solved at the Premium Live Event on February 15th. It's unknown yet if it will be used to introduce somebody brand new to the show, or form part of a repackaging for an existing member of the NXT roster.
Naturally, this has also resulted in speculation that those from the past with a penchant for hacking are responsible. Longstanding independent and TNA/Impact favourite Sami Callihan has been name-checked based on his own NXT history a decade prior as the slightly confused Solomon Crowe. He was known for hacking into da mainframe but the persona never really matched up with the vignettes when he hit the ring.
Similarly, Mustafa Ali was somewhat infamously cast as the SmackDown Hacker in early 2020, using hidden cameras to delve into the secret lives of Superstars and cause problems as a result. This was folded into the reveal of him being the leader of the woeful Retribution stable later that year. As a full-timer with TNA, Ali at very least has access to the side door created by the working relationship between the two companies.
All, seemingly, will be revealed at Vengeance Day.