He moves to avoid the fireball- it comes close enough that the hair on his forearm burns away, and he's going to need to have that seen to. Perhaps they ought to have cast their illusion and then sent the fire, because for several moments he's stuck in place, staring at things long banished from this world. It's not real- he knows it's not real- but it disturbs him still. He comes from it aware of the burn on his arm and with his teeth clenched tightly.

Drawing on his Craft doesn't require a waving of hands or any gesture at all. And Thranduil's not inclined to throw horror back at them- he simply takes their sight, replacing it with darkness, glamouring the whole tunnel as unending night without any stars.