Bilfur chants a few words in the ancient Druidic language, and the centipedes begin to glow with a violet fairy-light, making them easier targets!
Dougal's slingshot is good enough to kill one of the advancing centipedes, but Kiplyn absolutely destroys one of them with a perfect bullseye shot.
The remaining 4 centipedes attack the front-line fighters, nipping ferociously at their ankles! Willie kicks two of them away, and Dame Simonetta is saved from their venomous bite by her armor.
Dame Simonetta's attacks are ineffective, but Willie pulverizes one of the centipedes with his warhammer.
Wilbur guards the party's rear. He doesn't see anything within the 30' radius of lantern light, but he reaches out with his keen hearing... There! At the very limit of his earshot, he thinks he can hear a faint scratching sound, like fingernails or claws against stone.
This concludes Round 1. 3 glowing centipedes remain in the fight. They are locked in melee, so no more missile attacks. What do you do next??
Bilfur's Faerie Fire spell affects up to 12 linear feet of creatures (for example, two 6-foot humans, or four 3-foot hobbets). Six one-foot centipedes easily satisfies that requirement. They do not get a saving throw. The glowing centipedes are visible up to 8" (more than twice the range of lantern light) and attacks against them are at +2 to hit. Bilfur did not specify the color of the light, so I will determine randomly: 1d3 = violet.
The sling attacks also get an additional +2 to hit due to the short range.
Dougal 1d20=11 hit for 2hp, kill
Kiplyn 1d20 = 24! hit for 6hp, kill
Melee attacks, party loses initiative 1-5
2 centipedes vs Dame Simonetta: 15, 12 both miss
2 centipedes vs Willie: 9, 10 both miss
Dame Simonetta (two attacks, +2 faerie fire bonus): 4, 7 both miss
Willie (two attacks, +2 faerie fire bonus): 6, 15 one hit for 4hp, kill
Wilbur's Listen check 1d6=? (rolled behind the DM screen)