Tolerance Is Extinction - Pt 2 - S1-E9
Trivia: When Rogue is joining Magneto, she hyperbolically mentions Morph being a member of the X-Men for 30 minutes before being killed. This is a reference to Morph being killed (though, later brought back) just a few minutes into the second episode of the original series, which would have been around 30 minutes of total runtime.