How to defeat the Finns... maybe use cuendillar?

"Courage to strengthen, Fire to blind, Music to dazzle, Iron to bind."

Maybe the riddle refers to cuendillar. To make cuendillar you require three Powers ... Earth, Fire and Air in two separate weaves.

Fire is referred to directly in the riddle. Music and sound is always woven from Air in the series. Iron represents the Earth required to bind it, as well as the fact that Iron is the base substance to make it. As for courage to strengthen... it's known as Heartstone, and perhaps this is why.

We already know that the separate entities are forbidden, and they ask Mat this specifically. When Rand enters with a sword of Fire, they shy away. Cuendillar may be the cheat for the game, the ultimate key to ward them off while they rescue Moiraine.