Right click player name → Report → Botting.
This makes me think of the DE in Caledon Forest where you ‘harvest’ fireflies to make streetlights; and then have to kill a bunch of mosquitoes that are attracted to the lights.
Cluster bomb also has a DoT component; but yes, I believe hitting everyone and everything is the best bet for badge/loot drops.
I’m not sure how useful each class’ effect is, but jumping from a wall in WvW is enough to trigger it so some people might like jumping into an attacking force as a warrior for example and knocking a bunch of people back.
Something you might not like about thief ranged attacks is that aside from Cluster Bomb (shortbow No. 2), you have a max range of 900 instead of most ranged things’ 1200.
Ember is in the negotiation tent at Summit Waypoint in the Fields of Ruin.