Here the goal is to slaughter a bunch or orcs without getting hit. I mean, that's always kind of your goal, but here there's a tangible reward for. Your optional objectives are to slay 8 orcs with a single grog or firepit explosion (easy), and to do it all under the time limit (harder).
If you're saving Focus for other things, the grog barrels pack more than enough punch to meet the first optional objective- they actually have a surprising range. Just rile up a few orcs and shoot as they're passing by a target. There's a barrel and firepit handy right by your starting spot.
Getting under the limit depend on your favored playstyle- this is one of the few Shadows missions where there really are multiple different ways to win. Elven Rage is certainly a help, Shadow Strike will help you cover ground, and chained wraith attacks clear grouped enemies almost instantly. If you prefer to go loud, upgraded versions of Elven Light and your instantly lethal countermove can go a long way, with the added benefit that the orcs coming running to you.