For those who want a bulletproof strategy for Yiazmat:

[Crovii]

Let's say you don't want to go through the hassle of obtaining all the super weapons, which I personally didn't want to do this time around on PC. I did it at Lv 65, but Lv isn't that important.
Here is what you have to do:

Get the skills Wither, Addle, Shear and Expose. Then set Gambits like this:

Gambits for your Foebreaker:
-Ally Any: Phoenix Down
-Ally Status Petrify: Gold Needle
-Ally Status Stop: Chronos Tear
-Foe Any: Wither
-Foe Any Addle
-Foe Any Expose
-Foe Any Shear
Foe Any: Attack

Gambits for your Healer with Sage Ring:
-Ally Any: Arise
-Ally Status Reflect: Dispel/Dispelga
-Ally HP < 60% : Curaja
-Ally Status Petrify: Gold Needle
-Ally Status Stop: Chronos Tear
-Foe Any: Dispel
-Ally Any: Bubble (optional)
-Foe Any: Attack (I had Dark Shot as Wm/Mach, if you use a Staff don't bother)

Gambits for Red Mage with Black Robes:
Ally Any: Rise/Arise (depends on your Esper choice)
Ally Status Petrify: Gold Needle
Ally Status Stop: Chronos Tear
Ally Any: Bubble (optional)
Foe Any: Addle (if you have it)
Foe Any: Darkga

Gambits for your Bushi with Genji Gloves and Masamune:
Self: Bacchus Wine
Foe Any: Attack

That's basically it, no more in depth strategy necessary.

Now go in and start with Wither and Addle until those skills don't hit anymore, best done with 2 chars simultanously, but one is also enough. Go to Gamit menu and grey them out afterwards and do the same with Expose and Shear until they stop connecting. After that switch the Breaker for the Bushi and that's it. If your char has both jobs just switch Gambits.
You could go with Hastega, Shellga, Float and whatever fits your boat, but you won't need those and you'd probably have to watch your MP. Fight should be over in about 1-2 hours at speed x4. Don't leave the are though, or you'll have to break him again.

[UIY]

You can speed this up to a 10min fight on 4x speed with a Yagyu Darkblade and black robes, genji gloves and berzerk.

[Crovii]

You can do a lot of things to speed this up, but getting the blade is annoying and I bet alot of ppl have locked themselves out of using it. This works every time with or without the blade.

[UIY]

Originally posted by Crovii:

You can do a lot of things to speed this up, but getting the blade is annoying and I bet alot of ppl have locked themselves out of using it. This works every time with or without the blade.

It can be annoying to get yes, Bombshell is a bastard, but really as long as you have a dark damage dealing weapon or spell Yiazmat is a pushover once you break all his stats.

[初陽]

Yiazmat is pretty easy once you have breaks. Regardless of having a DPS job or not as long as you have a WHM and good MP sustain gambits.

Just a tip if you have jobs that can get shields have them equip shell shields, why? It halves chances of being stopped + insta-killed(shellga also expensive to cast). MagEva/Eva is useless vs Yiazmat so having other shields equipped is pointless. Only thing that could really kill you rarely is when hes CT time gets lowered and spam his normal attack that has a chance to OHKO you when hes at critical. If RNG blesses Yiazmat you're ♥♥♥♥♥♥.

If you can leave without doing anything but let gambits do its work for 1-2 mins then you can literally AFK away until he dies.

[Hinnyuu]

Breaks make every boss fight a joke. It's fairly ridiculous they made bosses susceptible to Wither/Addle, but here we are.

[Sh1nRa358]

yall lucky this isn't the american version Yiazmat lol
Japanese yiamat is hella easy. Don't even need a strategy.