This mission is found by backtracking from the start of Mission 15 to the room with the rotating spiked floor near the start of Mission 14. After descending in the elevator, examine the skull engraving on the wall to the right to begin the mission.
This mission tasks Dante with defeating three Shadows in this extremely confined space, for a Blue Orb Fragment. Dodge immediately when the mission starts, since the Shadow that comes out of the engraving starts a Guillotine attack during the introductory cutscene at extremely close range. Try to stay at the starting end of the corridor as this will generally stop the other two Shadows from getting involved.
The ideal tactic here is to attempt to get critical hits on the Shadows by firing Devil Trigger charged shots from Ebony & Ivory after jumping on the Shadow's spear attack. Regardless, try to avoid leaving the cross-corridor, as the spiked floor is still in motion and trying to keep track of both it and the Shadows is extremely difficult.
If attempting this mission in New Game+, Nightmare-β can be useful here, especially if charged, since it very quickly exposes the core of a Shadow and in this confined space it can easily damage all of them at once.