Excuse to blather about character motivations
*cracks knuckles*
So this depends on what Xan we're talking about. Current Xan, pre-flesh horror Xan (I know it isn't this one), first flesh horror Xan, or second flesh horror Xan.
Original Xan, pre-flesh horror: Basically a few steps away from an animal. No social skills whatsoever, runs mostly on survival instinct and greed. A bit of rational thought, but not much. Considers natural state of all life to be death, and given the opportunity will endeavour to convert alive people over to this natural state. He doesn't consider himself alive either due to not really having realized it. Desires essentially to convert life over to the natural state and for more power. Generally panicks under pressure, lashes out at full force with all he can muster. Very easily pissed off.
First flesh horror Xan: More developed as a person; considers himself a step above everything else apart from the Doctor, who he reveres almost as a god, and the AM who he knows could squash him like a bug if she wished. Incredibly arrogant, think kinda Semi-Perfect or Perfect Cell from DBZ. Basically classic villain, arrogant, cruel, hunger for more power, immortality, etc. He'll generally drop at least one new clone of himself on each new planet he gets to in order to ensure that if he's destroyed he survives in some manner. He has some capacity for social interaction if the people impress him through durability or sheer luck (see his quasi-friendship with Stacy). Possesses the capacity for subtlety, but not really all that much and he prefers to assume intimidating forms. He's better at responding to pressure than pre-horror Xan but if something's obviously about to kill him he'll drop everything and escape as fast as he can. Selfish, megalomaniacal, arrogant, cruel, with a strong self-preservation instinct.
Dan (called such because I disguised myself as a guy named Dan): Basically the above but seriously tempered by the revelation that he died by being incautious. Way more subtle, etc. Still has some trouble with social interaction, but he can effectively disguise himself as a random person if he needs to. Basically the above Xan but smarter.
Xanessa: If pre-horror Xan was a low-functioning sociopath, Xanessa's a high-functioning example. Totally cool under pressure and able to recognize when to run away and when to fight, able to keep up a convincing false identity for a prolonged period of time, etc. Keeps a running tally of those who have done her wrong and intends to repay them at a future point. Has an end goal that you likely know from my PMs on the subject. Also instead of seeing the Doctor as a god like the other versions of Xan, sees him as a very skilled and very dangerous individual, worthy of respect but not blind admiration or devotion. Intends to study under him at some point.
I keep a lot in my head.