First, Meta Knight pulls out his cape. If he catches a character, the character will be paralyzed. The screen will then fade to black, freezing everything. Meta Knight then says "Behold... know my power!" and hits the trapped character(s) and any others who are in range with a powerful slash, cancelling out the gray effect and launching fighters who were hit.
If the user attacks quick enough, they can cancel all the knockback of the move with another attack.
On the ground at high percentages the move will glitch and bring you to your standing position, while you fly in the air. This only happens at higher percentages, and is therefore a KO unless a wall blocks you, or you momentum cancel extremely quickly.
Even if a wall blocks you, you'll be stuck on it at "high speed" for at least a full second, giving the Meta Knight user enough time to charge up a smash or rack up damage.