They Vortigaunts did not come from Xen but they fled there to escape their Homeworld once the Combine invaded it, they were enslaved there. Describe what a Vortiguant looks like (Detailed description)
A Vortigaunt looks like a humanoid creature with two legs and three arms one of the arms comes from it's stomach. Vortigaunts have dark green skin and tall, thick legs. Vortigaunts are slightly hunched over. Vortigaunts also have some crooked teeth coming from it's mouth, above it's mouth it has multiple red eyes. What were they while on Xen?
They were an enslaved race on Xen, they were enslaved by Nihilanth and they were forced to fight for him. What is the Vortessence? (Detailed description)
Vortessence is a way of communication between Vortigaunts, they can also sense future events and can take power from objects, they can also to increase their powers with an Antlion extract. What were they doing in Black Mesa? They were sent to Black Mesa by Nihilanth to attempt to attack Earth and enslave the humans as well during the resonance cascade, multiple other creatures from Xen were also sent to Black Mesa. Do you agree if you get dewhitelisted from the whitelist you're allowed to reapply once then you will have no chance of getting the Vortiguant whitelist do you understand?