The allied army of the guilds are nothing to scoff at as they were easily fighting against the Foliage Soldiers and the numerous versions of them. They were able to surround the Forest Swamp Abomination and thought they would be fighting it, but it was different from what they expected. The Forest Swamp Abomination did not fight but would create numerous Foliage Soldiers.
The Foliage Soldiers all came from the body of the Forest Swamp Abomination as they were being recycled. Every time they kill one Foliage Soldier, the body of that monster would then be sucked back to the Forest Swamp Abomination to be recreated to another monster variant of the foliage series. They thought that this would once again be a battle of attrition, but they noticed that the production of these monsters started to slow down with the more they kill.