The idea is to give Deadly and Killer to units that deal damage effects and benefit from attacking constantly.
Feel free to discard wisps, treasures and sigil cards to keep the pressure going.
Clodagh is most useful once you hit 6 Fire influence, so try to reach that as soon as possible. But in the later game, casting Treasures with 1 or 2 Clodaghs on the board can turn your wisps (and everyone else) into a massive threat.
We have 3 units that create treasures here:
3- Desert Alchemist
EDIT: Added 3 Autotreads because of the obvious and extremely powerful removal synergy with Touch of Battle