As stated above any can variation is better then Mournful due to the unbreakable damage, combo potential from can, ads, sharpen, party and reflect.
Mournful IMO IS the rushdown variation. Due to the buff to RB ExAirglaive has gotten stronger.
Example: f112-Rising Blades, exfloat, ji4 (delay to bait some armor, pokes, and backdashes) ExAirGlaive. You just need 5-7% chip into a mix up which on hit can lead into 30-35% do all in all you just got 40% for two bars and you keep your turn. And it's all mostly safe...cant beat that with a stick, then with staff grab being plus 27 you have all the power on Oki. IaGlaive, b2. B3-ExGlaive, b3-RBxxExFloat-etc. B12-RBxxExfloat, jip2, b3-ExGlaive.
Or my favorite corner your not getting out chip out situation:
F22u4-GLAIVE, land, EXRisingBlades-Exfloat, jip2, f112-RBxxExfloat, jip2, f112-Shadow Kick.
Or if they have no meter and you wanna swag out and get evwn more chip:
F22u4-GLAIVE, land, u2-float, jip2, f112-RBxxExfloat, jip2, f112-RBxxexFloat, jip2, f112-RBxxExfloat, jip2, f112-ExGlaive, f22u4-glaive, land, d1-Shadow kick or staff grab. It's so fun it's should be illegal.