Ben 10: Ultimate Alien Episode 1.15 Perplexahedron

Azmuth, displeased by Ben's failure to protect the first three pieces of the Map of Infinity, teleports Ben, Gwen, and Kevin to the fourth piece's location: a deadly artificial planet known as Perplexhahedron, created by Professor Paradox to destroy anyone who enters it. Ben, Gwen, and Kevin manage to fight their way through the traps and reach the maze's guardian, the Sentinel, who gives them the piece. When the piece is taken, the whole planet starts to fall apart. The Sentinel stays behind, content that he has fulfilled his purpose in life, but Ben insists on rescuing him. However, Aggregor has found the Sentinel by the time Ben returns, and in the ensuing battle manages to take the final piece of the map from Ben. The Sentinel, dismayed that his life amounted to nothing, vanishes into thin air. Though they've lost the battle, Kevin assures Ben that the war isn't over. NOTE: Ripjaws appears briefly in this episode.