Post your best magic-related home-brew here. I'll start things off:

Bardic Warcry - 3rd level bard spell. Range, 50 foot sphere, to enemies it has the effects of thunderwave and to allies the effects of heroism.

Since no one's posting:

Korred Jig - 7th level, available to warlocks and bards. Range: 100 feet. Targets gain disadvantage on attack rolls as they fight the rhythm of the jig. If a target fails their Charisma saving throw to end the effect, you gain the ability to redirect their attacks when they miss, making them reroll the attack, without disadvantage, against a different target within range. If they fail two saving throws, they become mindless puppets controlled by the dance. They do their best to protect the caster but otherwise they can't be commanded. This last effect can only be cured by greater restoration or magic of similar potency.