The correct answer is: B. Shawn Michaels
At the 1994 Royal Rumble, The Undertaker defeated Yokozuna in a Casket Match. At the 1998 Royal Rumble, The Undertaker defeated Shawn Michaels in a Casket Match.
A. Yokozuna is incorrect because he was The Undertaker’s opponent in the 1994 Royal Rumble Casket Match.
C. Mabel is incorrect because he was The Undertaker’s opponent at the 1995 King of the Ring.
D. Triple H is incorrect because he was The Undertaker’s opponent at the 1997 Bad Blood.