[Trigger] {Spell Request} - Dark Arrows - An Attack modifier with a chance to cause a spell

[Griffith]

{Spell Request}

I want to make a attack modifier spell like (fire arrow, cold arrows) Called Black Arrows.

basically this spell acts like fire arrows were it gives bonus damage to attacks, but I want it to have a chance on hit (like 25%) to Curse the enemy, Like Undead Banshee Curse.