Marth (SSBM)/Up special
Although relatively situational, Dolphin Slash is a highly rewarding move with a strong surprise factor if timed intelligently. The move's active hitboxes start on frame 5 where they hit the strongest and end on frame 10 where they are more disjointed but hit much weaker. Like most of Marth's attacks, this attack has a tipper hitbox that deals the most knockback with the most favorable angle if the hitbox farthest away from Marth's body connects. With the sweetspot's considerable disjoint, speed (faster than a grab), and its one frame of invincibility, it is one of Marth's better out of shield moves although it is his riskiest. Additionally the disjoint is longer than the move's animation would suggest; doing it out of a dash dance or a tech chase can catch many people off guard and will often KO very early since opponents likely wouldn't DI it properly. The move's primary usage though is a combo finisher, having very similar setups to a Ken Combo. More often than not, an opponent DI'ing to avoid the Ken Combo will DI directly into a Reverse Dolphin Slash instead. The move can also be used to edgeguard recoveries with long periods of vulnerability such as the charging period of Fox's/Falco's up B, or the ending lag of an aerial Falcon Kick.
As a recovery option, Dolphin Slash is considered subpar. Its speed makes it difficult to hit Marth out of without ledge invincibility and has a disjointed hitbox above Marth's head which can hit through the stage and punish people standing near the ledge. However the move doesn't travel far horizontally at all and although it can be angled, the extra horizontal distanced gained often isn't enough. Additionally the move's hitbox duration is short and as such is very easily edgehogged. The move is also infamous for having a technique (aptly named the Marth Killer) developed to specifically counter it. If an opponent rolls to the edge and angles a light shield away from the stage, the late hitbox of Dolphin Slash will hit the light shield and the resulting shield push will put the opponent directly on the edge, setting up a perfect edgehog.
Overall, this move's advantages over Marth's other finishers (f-smash, Shield Breaker, and down air) come from the move's speed; the move is without question Marth's fastest strong single hit punish. But the move's biggest drawback is how punishable it is when whiffed. The slow falling speed of the descent as well as the move's landing lag often spell death against a competent player.
* Marth reverses if and only if the control stick is held backwards between frames 5 and 6.