There is still Ex Guarding in Duodecim...

[Nexus_Nocturnal]

I did this by accident against Sephiroth while trying to use Ex Revenge. I did an HP Assist Switch an then went to R+Square a split second later. Result? I was in EX Mode in front of a Staggered Sephiroth, free to do whatever I wanted. For some reason, going into Ex Mode stopped Kain from flying to the top of the screen like he should after an Assist Switch.

My analysis...

When you use R+Square to Assist Switch, it causes your opponent to Stagger instead. (It also doesn't lock your Assist Bars)
Apparently the second you use an Assist Switch you are no longer considered being hit or staggered.
Going into Ex Mode stops your movement instantly.

With a full Ex Bar you can Ex Revenge
With a full Assist Bar you can Assist Switch
With both full bars, you Can Ex Guard like in Dissidia 1.

EDIT:

Upon further testing, it might have to be done during an enemy's HP attack. It seems HP Assist Switch doesn't stagger BRV attacks.

[Nitron X]

Hm.
Should be a lot less broken, however, than in Dissidia 1, due to the higher difficulty of getting it all.
plus the skill to do it, even if it doesn't seem to take much to do, besides the timing.
I guess it'd be a bit of a reward, then?
especially since either can be instantly depleted by the opponent using the other gauge.

[holy0crux]

We've known that Change 2 never caused Locks, but are you sure it's for HP attacks only? Maybe you should try on Jecht...

Ujhbn said that Change 1 TAKES the hit while Change 2 attempts to BLOCK the hit...

And I think that the whole Change 2 > EX Mode should be totally viable. You've earned your share of Assist and EX, so you can choose to use it however you'd like.

[Nexus_Nocturnal]

Maybe I'm not doing something right, but sometime when I do HP Assist Switch the opponent will stagger, and other times not. Maybe if they move past the attack too fast they don't stagger, because it apparently didn't stagger Cloud's Climhazzard.

Also, I might have done something different to stop Kain from moving, because Kain keeps flying up after going into EX Mode. Maybe I'm just not doing it fast enough or maybe I unknowingly did something against Sephiroth that stopped my movements.

One thing is for sure though, that first time I got it to work I got the exact result an Ex Guard in Dissidia 1 would give.

[holy0crux]

Make sure to keep track of ranged and melee, and to look for WHEN the Assist blocks.

Changes happen when the character is staggered at any time, even if it's just a clash between moves. Are you Changing while your character is staggered? Maybe you're just mistiming the blocks... Try Change 2 blocking Onion Knight, rather than Cloud.

[Nexus_Nocturnal]

I'm pretty much spent for tonight, but I'll make sure to keep on testing tomorrow. Onion Knight sounds like a good candidate to practice on, and I seem to run into him a lot in Arcade xD

[ujhbn]

Maybe I'm not doing something right, but sometime when I do HP Assist Switch the opponent will stagger, and other times not. Maybe if they move past the attack too fast they don't stagger, because it apparently didn't stagger Cloud's Climhazzard.

This is because the blocking frame of [] Assist Change last for a very short time. Therefore if you try to do that when attacked by say, Slashing Blow, Radiant Wings, you have to do it right before the next hit lands in order to block it.
While quick continuous hits like OK's melee attack is easily blocked by the [] AC.

Anyway, very nice find.

[Nexus_Nocturnal]

It would be a lot easier to test out if EX Force wasn't so hard to get in Duodecim xD

Well, I got OK up as an opponent, so I'll be testing against him for awhile till I find how to do it perfectly.

[Narolf]

Tried this for more than a hour now and I didn't manage to stop the character's rising after the hp AS. I'm having a hard time to figure when I have to go into Exmode and wonder if it still works when you hp AS while being close to the ceiling, when the character is supposed to fall after the hp AS you know.

I shall leave the infinite Ex's and assist's gauge Cwcheat's codes.

_S NPJH-00069
_G Dissidia Final Fantasy 012 Prologus DEMO [JAP]
_C0 EX9999
_L 0x6039B464 0x461C4000
_L 0x00020002 0x00000018
_L 0x2000054C 0x00000000
_C0 ASSIST GAUGE MAX
_L 0x6039B464 0x461C4000
_L 0x00020002 0x0000001C
_L 0x2000054C 0x00000000

[Kraid]

The problem with this Ex-Guard is that it is way to situational AND requires really good timing. So really this is not a problem at all. EX is harder to get as well and with EX builds, Assist becomes harder to get.

So it doesn't matter if Ex-Guarding is in Duodecim to be honest. This isn't really an 'Ex-Guard either', more like a 'Assist guard into Ex' or something like that.