You need to beat the Undertaker or Retro Undertaker in the Defeat the Streak mode with 10 of his past victims.
Here is the list and when you unlock some of them in the 30 years of Wrestlemania mode.
King Kong Bundy (WM 2)
Diesel (WM 10)
Kane
Triple H
Big Show or Tensei/A-Train
Randy Orton
Edge (WM 22)
Batista (WM 23)
Shawn Michaels
CM Punk
That's the 10 victims for the trophy.For some reason, you can't use Ric Flair (WM 18) and Mark Henry (WM 22) . Jimmy Snuka, Jake "The Snake" Roberts,Giant Gonzales, Sycho Sid and Big Boss Man are not in the game.