Thorne moves up and retrieves his shotgun rather than the rifle he so lovingly maintains. Aiming low and to the side of Andrinor, he fires both barrels at the swarm.

Spoiler: OOC
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Okay, so scatter weapon rules are weird, especially when one tries to match them to the weird rules governing swarms. A scatter weapon affects every target in a cone area, but instead of a reflex save or something of the sort, the shooter rolls a separate attack roll for everyone within range.

So, when we look at the RAW for swarms:
-because it affects an area, swarms take +50% damage.
-but its a weapon, so swarms take -50% damage if they're tiny critters, and none at all if they're smaller than that.

The latter bit makes no sense in this context. Sure, stab a swarm with a dagger and you're not going to do anything, because at best you killed one out of hundreds. But shoot a swarm with a shotgun and you're going to hit a lot more than one individual in said swarm. Not least because if they weren't being treated as one entity for convenience, by the rules I'd be rolling attack rolls vs the AC of every single individual member of the swarm (not that any of us would want that)

I'd be inclined to split the difference, have scatterguns be one of the few nonmagic things that work fine on swarms, with no bonus or penalties to damage. But that's not my call, so for now at least, I'm just going to roll two scatter shot attacks and damage, and let the DM decide how to apply things. If they do very little, oh well, learning experience for Thorne not to try that again. To confirm I'm hoping to catch half of the swarm in the AOE without touching Andrinor.

Note that the double barreled shotgun has two enchantments on it, the shocking property and the limning property. The latter outlines struck creatures in an effect similar to faerie fire for 1 round

Barrel #1 attack (1d20+30)[39] damage (1d8+15)[20] electric damage (1d6)[4]
Barrel #2 attack (1d20+30)[46] damage (1d8+15)[23] electric damage (1d6)[6]