Welcome to Librarium Online!
I dont play Eldar, but my friend does, and wants me to ask this question.One of its rules say Daemon, does that refer to the Chaos Daemon Codex? Does it make it immune to instant death (What started this was my Swarmlord Killed his Avatar in one hit, thanks to Bonesabers, and hes wondering if that really works on the Avatar)
No, it isn't
The Avatar's Daemon rule does exactly what it says it does in his entry-- i.e. 4++ save and vulnerable to abilities that affect Daemons.