text: His first feud came against The Undertaker, and began after Heidenreich ran in during Undertaker's WWE Championship match against John "Bradshaw" Layfield at No Mercy. Undertaker beat Heidenreich at the next month's Survivor Series, but again Heidenreich cost him a WWE Championship match at December's Armageddon when he interfered in the main event fatal four-way match not once, but twice. At WWE Tribute to the Troops on December 23, Heidenreich lost to the Undertaker via countout. On the January 6, 2005, episode of SmackDown!, Heidenreich and Heyman lost to the Undertaker in a 2-on-1 handicap match, after Heyman was pinned. After the match, Heyman was placed in a casket by the Undertaker, writing him off television.
  At Royal Rumble on January 30, he faced The Undertaker in a casket match. Midway through the match, Snitsky from the Raw brand interfered on Heidenreich's behalf. However, after opening the casket, it was revealed that Kane was hidden in the casket, who pounced on both Snitsky and Heidenreich; they continued their fight in the crowd, while Heidenreich lost the match. This started a chain reaction of feuds, originally planned to lead to a match at WrestleMania 21 in which The Undertaker would partner with Kane to take on Snitsky and Heidenreich. This idea was later nixed; Undertaker instead fought Randy Orton and Kane was placed into the Money in the Bank ladder match. The feud between the four instead culminated at a live event on February 6, with Undertaker and Kane getting the win.
  Teaming with Animal and departure (2005–2006)