This idea started out as a simple play on words, but I kind of like it for a low-level swarm encounter.
Hellfire Worm (Level 1)
The scent of fresh rain and brimstone heralds the arrival of the hellfire worm. A foot long, and colored with reds and oranges that shift like coals, this is no ordinary earth worm.
Attributes: Energy 3
Defenses (vs Fire): Toughness 10 (16), Guard 10 (16), Resolve 10 (16)
HP: 1
Speed: 5’ Crawling, 10’ Burrowing
Size: Tiny
Favored Actions:
- Hellish Blaze - Energy (1d20 + 1d8 Fire) vs. Guard (triggers Persistent Damage (1d4 Fire) on 1 damage or more
Feats: Superior Bane Focus (Persistent Damage), Energy Resistance II (Fire)
Strategy: Attack in groups, burrow underground when frightened
Edit: applied @Great_Moustache’s excellent suggestion for listing energy resistance defenses with the defenses section.