From SmashWiki, the Super Smash Bros. wiki
Overview
Marth does a forward vertical slash from top to bottom with his sword, doing 8% damage on the base of the sword and 11% with the tip. Although it has low knockback if hit on its base, it has good KOing potential at around 120-130% when hit on the tip, and can KO earlier when used near the edges of the stage. Hits with an arc which covers his entire front body within frames 6 to 8 and can autocancel in a short hop. It is a useful move for spacing, edgeguarding, and as an aerial approach tool due to its long-ranged, disjointed hitbox. It is a decently safe move in neurtal when spaced near the end of the sword, but only when used immediately out of a jump (be it short or full hop) and is a great retreating. However, unlike in past games, it cannot be interupted with another aerial during a short hop. It also has 16 frames of landing lag and strict autocancel frames, making it unsafe to land with this attack. It also has low hitbox duration, making it require precise timing to consistently space with it.
Timing
Attack
Hitboxes
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6-8
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Ending autocancel
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36
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Animation length
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38
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Landing lag