[Varyon]

One important question to consider is how flaming weapons would interact with the acidic blood. Would the flame aerosolize the blood, making it even more deadly, or would it essentially cauterize the wound, preventing any from spraying on the fighter? How about icy weapons - might they freeze the wound, preventing bleeding? This is likely to have a large impact on how well the characters can handle the xenomorphs in direct combat. Characters using indestructible gear (made from orichalcum, dragonbone, or similar) may have a better time of things.

Of course, the xenomorphs may not opt for direct combat. Don't forget, these ones spawned from goblins, meaning they're likely to be a bit shorter (although this will depend on how short goblins are in the setting; at least in GURPS DF, they're only a couple inches shorter than humans), and will probably be more cautious. I'd expect them to be more inclined to the stealthy approach than human-spawned ones, even when they have the numbers. They'd likely stalk the delvers until they let their guard down, at which point one or more will pounce, snatching up whoever they can to take back to the nest (and those that struggle too much suffer an armor-piercing bite to the Skull, complements of the xeno's mouth-tongue). I could easily see them expanding to a nearby village (a goblin lair always needs a nearby village to raid, at least for the delvers to hear about it), and from there spreading like wildfire, if the delvers don't stop them here. Of course, magic can help them here - the xenomorphs are susceptible to fire, and various warding/detection spells may make it difficult for them to get the drop on the party.