Byleth (SSBU)/Down special
Byleth channels all of his energy into a sluggish but colossally powerful slash at 30% at its highest using the Hero's Relic Aymr. It has super armor during startup, can be reversed, and Byleth can drop through platforms while performing it. Like other "bold" moves (such as Falcon Punch, Warlock Punch, and Hatchet Man), it triggers Special Zoom. When successfully executed, Aymr can break shields in a single hit. When it is used successfully while falling off the battlefield, by an edge, and it hits the battlefield, Byleth will be suspended, ending the fall. Much like the aforementioned "bold" moves, it expectedly has extremely high lag all around in exchange for its power, making it a very risky yet rewarding move mainly used for hard reads. Byleth may occasionally yell "A...ymr!" while using this move. When used in the air, Byleth is stalled slightly just before the hitbox comes out. The animation itself is based on Flickering Flower, a combat art learned exclusively by Edelgard once mastering the Emperor class in Three Houses.
The shockwave hitboxes function like Hand Slap. They will match the ground they impact. Aerial shockwave implies that the axe was planted into a platform as Byleth is airborne.
The timing implies Aymr doesn't touch the ground. If it does, a shockwave hitbox appears on frames 3-6 after impact.