From SmashWiki, the Super Smash Bros. wiki
Unwavering Chivalry is a single-player event match in Super Smash Bros. for Wii U. The player controls Meta Knight and must defeat Marth without KOing Peach or Zelda. Defeating either Peach or Zelda will result in a failure.
This event is unlocked by clearing Robotic Rampage. Completing the event unlocks the up path.
Clearing the event on hard difficulty awards a Vengeful Mask equipment.