I kno this isn't technically a "share your headcanon" thread, but since there's no other place to put the following thought, well...
My headcanon is that the Deacon is a Xeno who's really shit at being a Xeno. Like, he can bleed acid, but it's only potent enough to give you a bad rash. He can headbite with that big ole' jaw, but it'll just feel like a really strong finger poke. Building a hive is like... he pukes up a bit of slime and wipes it on the wall. If he tried to pull off the "climb through the ceiling" trick from Aliens, he would just end up getting stuck and falling through the AC duct. Then he would get up, trip, get up again, and run behind a table; Ripley and co. would pretend not to see him out of pity.
He is bad at being an Alien, but damn it, he's doing his best.