Trap spell

[marc]

Did anyone find a sure way to get the trap spell?

I'm at the 3rd island and I didn't find a copy of that spell yet. The problem is that, playing on impossible, the stacks start to get really high after a point, making getting a "last hit" with a trap spell problematic.

I'd like to get started on that trap medal ASAP, as the bonus traps on the battlefield are just incredibly useful. Not only do they do damage, but, more importantly, it makes the unit lose its attack for the turn. It was my favorite medal in AP and I'm worried I won't be able to get it in WotN.