So Sin did indeed call in reinforcements. I'm very curious about who it's going to be since Sin seems to be connected to Liones and Nakaba's recent statement hinted at a familiar character showing up. If the title of the next chapter is any indication then there's a decent chance it could be Tristan, but I suppose it could also refer to Percival. The attack that was used to destroy the monsters looks like some sort of a projectile made out of energy, which would fit the idea that Tristan was the mystery archer who killed Talisker's fairy thing. If it's not Tristan then the only option I can think of is Gilthunder, since you could interpret the energy projectile as him covering his body in lightning and then blitzing all over the town kinda like he did when fighting Meliodas and also similar to what his father did when fighting against Fraudrin.