From SmashWiki, the Super Smash Bros. wiki
When activated, Meta Knight gains an extra pair of wings, lifts his sword, says "Know my power!" (思い知れ!, You shall realize!) or "Behold!" (見るがいい!!, Behold!!), and summons a lightning bolt that creates a cross-shaped burst. If he traps anyone, he'll then proceed to slice the opponent at multiple angles, similar to Great Aether, finishing with a final hit that launches the opponent sideways with a different camera angle if the attack was gained from a Smash Ball rather than through a meter.
This move resembles Upper Calibur, a move Meta Knight uses in Kirby Star Allies, with the addition of the extra wings and a flash of lightning as opposed to an ascending slash. The pose Meta Knight takes when summoning his sword is a pose commonly associated with opponents of his type, appearing as either a mere up stab or as a summoning act. The cross-lightning both resembles Meta Knight infused with the Zap element in Kirby Star Allies and the animation for Mach Tornado in Kirby Super Star Ultra. The pose he takes after landing the final strike resembles his Kirby Air Ride render.