The Instigator's Enchantment

I can place the enchantment you require on the banner quite easily, <name>. Unfortunately I don't have the materials I need as it is very rarely that someone asks for this sort of charm.

I will require the essence of one of the Eldreth ghosts that haunt these halls, a handful of Scholomance dark runes and some large brilliant shards. Bring me these reagents and I shall perform this task for you.

Have you gathered the materials I require, <name>?

Yes, these will do just fine. After I'm done, no force in the world will be able to stop your victim from accepting your challenge.