Xul is a great specialist and fantastic add to the Nexus. His kit and talents allow for diverse builds and playstyles based on how you like to build him or the specific game conditions. All builds are subject to situational choices. For intance, I personally think Shade is far and away the best level 1 talent because of how much mitigation it gives you, and just makes that ability feel so much more useful in a defensive situation Iit also blocks attacks from spawned minions e.g. hydralisk, not sure about ultimate based AAs such as banshee's or garg. If the enemy team has absolutely no AA dmg to worry about, then I might consider the others but even still I think evading whatever AAs come your way can mean the difference between life and death. As far as ultimate choice, you can use either ultimate in any of the builds, really just choosing poison nova if you think your team needs the dmg, or mages when you need zone control and don't need the dmg. Also, at level 20, if you take Mortal Wounds in any of the builds you should feel totally ok with that. It probably could be considered core on every build, so OP, awaiting nerfs.

Summoner
This is a great build designed to push. In the spirit of the build I chose all the skeleton talents, but you always should be ready to adapt depending on the map and opponents. Jailor seems fairly underwhelming, but it does give you a little bit of in combat sustain if no minions are around to make skeletons since it does trigger Rathma's blessing, and fits the spirit of the build best. You can take poison nova at 10 instead, and at 20 bone spear if you need a little more dmg for teamfights since this is a lane pushing build, or mortal wound because above.

Strong on: Tomb of the Spider Queen, Towers of Doom
Weak on: Sky Temple, Garden Terror,
Rating: *****

Ranged Poke
This build is designed to play Xul as ranged as possible, relying on your Scythe. It's actually a pretty easy skillshot to land, even with the extra range, since the enemy doesn;t have a lot of time to react to it spawning right behind them. Level 7 can really be any of the three talents you like, I stick with Rathma's here since Q can farm waves at range and get the heals from skeleton spawn while we sit back until we go all in if at all. At 10 we take mages since it keeps us safe and allows landing our Q's even easier. At 20 can always take Mortal Wound as an option, especially since we took reduced CD at 13, but I like bone spear for added direct dmg and ranged poking style that works with this playstyle.

Stong on:
Weak on:
Rating: ***


Melee Assassin
For those that love to play a melee style, this is the Xul for you. We're going to get in their face and do some serious damage. Since we are going for dmg, we are taking backlash at 1, but you can always opt for shade for more defense especially if you know you will be going toe to toe with a Thrall or Butcher. Jailors at 4 are just for a bit more dmg, any choice is viable here tho. Harvest Vitality a must, and since we are going for melee assassin we take poison nova. Giant's curse at 13 is best, but consider Decrepify if you are having trouble sticking onto targets. Vulnerability on our root is pretty core, and since we don't want anyone healing up after we did all this work to kill them, we take Mortal wound at 20. If healing isn't a problem, then consider Bone Spear for that extra bit of dmg for kill secure.

Strong on: Sky Temple, Battlefield of Eternity,
Weak on:
Rating: ****

CC Machine
Really depends on team comp communication, as you are trying to be as CC/Debuff heavy as you can so your team can follow up. Executioner at 16 to take advantage of all the CC you bring, or switch to Flowing Wounds to reduce cd on Q for max uptime on slow/mortal wound.



Hybrid