Trap spell
 

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.

I never found it hard to last hit units with trap. Even a stack of 200 Paladins will at some point be a stack of just a few, if the fight is to be won. That's the moment you put the trap right in front of them, who, (mis)guided by the AI, will walk right into it. You don't have to kill the units right away with Trap. Weaken the stacks by other means, then use trap.

i like that trap spell too, i got it on the second island from dig-up chest, but unfortunately I'm afraid nothing is certain in the stores or on digs, pure luck.
in AP i never come across phantom spell, i hope i will get that here sooner rather than later