Trapper medal

[Nirual]

It's definitely easier if you get the spell early and start using it aggressively right away. It gets easier after level 1 because the traps placed by the medal effect are usually much stronger than the spell ones (though they tend to spawn in rather useless spots).

I also recommend using elemental effects (poison/fire/frost) as much as possible as the periodic damage can't kill the troop entirely and is useful for softening them up.
Plus you get to work on Battle Alchemy at the same time