absolute best wallbreaker in the tier
...eh, not quite. It can struggle versus standard stall because Blissey just diddles on it for eternity, and against hyper offense it's usually just gonna either A) take a hit, kill something, and die or B) die. What it is good at doing though is smashing balance teams - their sturdiest Ice resist is usually bulky Arceus-Water which can be taken down by Draco Meteor, it obviously has coverage moves to take down Steels, and nothing else really wants to take Ice Beam especially considering fast Ho-Oh seems to be growing in popularity over bulky Ho-Oh.
Since you asked for thought processes I'll actually try making a team with it. So a good starting point for building with this mon seems to be pairing it with offensive stuff that can take advantage of weakened Ice resists. Fast Specs/LO is probably best here to take full advantage of Kyurem-W's power. I personally prefer LO for flexibility + Roost access, but either is fine.
One thing that actually sprung to mind as a partner is OTR Bronzong. It loves having fat Waters and Steels (Waterceus, POgre, Keys, Zonger, Aegis, Zor, etc) out of the way and it covers a ton of enemy threats (Lati@s, Mega Diancie, Xerneas, Salamence, Arceus-Ground, Groudon w/o Plume) at the same time, which helps make up for Kyurem-W being lame defensively. They are all good against the team archetypes the other is bad against, which is helpful for obvious reasons.
So we're starting with this:
LO Kyurem-W / OTR Bronzong
First, let's get the obvious teammate out of the way:
LO Kyurem-W / OTR Bronzong / Primal Groudon (set undecided, but will probably be the rocker)
After that it's pretty much covering the basics: hazard control and checks to PDon, Ho-Oh, CM Arc, EKiller, and Darkrai. I also want something else to help with the stall matchup because Blissey stalls look rather mean at the moment. We can help with hazard control, Ho-Oh, and the Dark resist by choosing Mega Diancie. Typewise it has great synergy with our main offensive core and is a formidable offensive threat itself, and it likes having Kyurem-W to wear down bulky Steels and Waters that are often its main checks.
LO Kyurem-W / OTR Bronzong / Primal Groudon (SR) / Mega Diancie
We can handle CM Arceus and Darkrai with CB Ho-Oh, which also doubles as a great stallbreaker in conjunction with the rest of the team. We're going to need strong anti-hazard support already with Kyurem-W on the team, so it's not big deal to include Ho-Oh.
LO Kyurem-W / OTR Bronzong / Primal Groudon (SR) / Mega Diancie / CB Ho-Oh
Our last slot absolutely has to be a Defogger, and it needs to be able to help against Primal Groudon, Ho-Oh, and EKiller. Looks like it's gonna be some kind of Arceus. This is actually a little annoying to work out though, as no Arceus variant covers all three of them as well as I would like. Wisp Dragon Arceus does come pretty close though. It's not the best EKiller check by any means and without Toxic it has some trouble dealing with Groudon, but I have Bronzong to act as backup against Fire-less PDon and Ghost-less EKiller, as well as Mega Diancie and my own Primal Groudon to help check Ho-Oh, so it can at least do what I need it to do.
LO Kyurem-W / OTR Bronzong / Primal Groudon (SR) / Mega Diancie / CB Ho-Oh / Wisp Arceus-Dragon (shoutouts Hack)
And that's what I ended up with. It feels alright, and Kyurem-W baits things that stuff like Rayquaza/Palkia don't so it seems like it has good offensive synergy here. That said, the shakiness versus EKiller is still annoying. Having Wisp non-Ghost Arceus as the only check isn't the best thing in the world, but the Arceus slot really needs the Fire resist for PDon/Ho-Oh so it pretty much has to be this. Stone Edge Giratina-O
might work over Dragceus but it can still be overwhelmed easily and not having an Arceus forme in ORAS is meh.
Using the Mega on Gengar or Sableye could also lead you into an interesting new direction, but Diancie has good synergy offensively with Kyu and I'm a fan of Diancie in general so...
Overall, building with Kyurem-W is very tricky as it has very little defensive synergy, not resisting much and requiring extensive anti-hazard support to make the most out of it. It also doesn't accomplish much against hyper offense due to said bad defensive typing and lack of boosting options. I tried though!
(also
hyw that team is too weak to geoxern)