The Undertaker returned to RAW by interrupting Elias’ segment.
Here is what happened in that segment (an excerpt from Mike Tedesco’s live RAW recap.)
“The bell tolls, and the crowd ERUPTS! The Undertaker’s music hits, and he makes his legendary entrance. Undertaker did not appear on WrestleMania last night for the first time since the year 2000. Undertaker magically turns the lights on and enters the ring. Undertaker is not wearing his eyeliner. Elias goes to leave while the crowd is chanting, “UNDERTAKER.” Elias then stops and reenters the ring. Elias removes his jacket and takes off his wireless microphone. A “Holy sh!t” chant picks up. Elias slowly steps up to the Dead Man, and Undertaker steps up to him. Elias turns to leave, but then he tries to blindside him. Undertaker quickly big boots him down before hitting a Chokeslam! Undertaker removes his trench coat before signaling for the end. Undertaker then drops Elias with a Tombstone Piledriver before posing over his body.”
— WWE (@WWE) April 9, 2019