Mission Failure is an event that occurs when you lose on a level.
Levels that it can happen on include Story mode, Challenge mode, and Arcade League. For it to happen, the player's character must either lose all of his/her health points, fall off a bottomless chasm, or possibly fail an objective.
When the screen is displayed, you are given the option to either restart the level (possibly from the nearest checkpoint) or exit the game. On the screen, you can sometimes view other menus such as the list of objectives that you completed and failed to complete, the number of points each character earned, or the briefing.
When the Mission Failure screen appears, somewhat drastic music begins playing.In Timesplitters 2, Voices can be heard when the music is sped up. This appears to be Captain Ash's dialogue from the beginning of the Aztec Ruins level.
"Now Now! Stay right where you are Golem! This belongs to me! Good lord. Ooof. Nooo! Take that you bounder! Take that you bounder! I'm off. Rugby's just not your game, is it?"
Also at the end of the track is the voice of a woman saying "Is that too loud?". This was either an accident or a joke by the developers.