6th Gen Critical Capture?

[Deja Vu]

Let me begin with saying that I never owned a Gen V game for various reasons, including lost ownership of my DS. However, I recently bought a 3DS and Pokemon X. I whizzed through the main game and eventually found myself at the end of Terminus Cave. After putting Zygarde to sleep and weakening it quite a bit, I threw a few Ultra Balls and, much to my surprise, the ball shook but once and darkened. I researched this phenomenon and it is apparently called a "Critical Capture". Does anyone know the chance of this happening? I was kind of startled that I may have accidentally selected my Master Ball after it happened, haha. Feel free to share any other Critical Capture stories.

 

[Hikamaru]

I've come across critical captures in both 5th and 6th Gen, but I heard the chances of getting one increase as you catch more Pokemon. It's not exactly known how often a critical capture occurs but they're usually distinguished by a "clang" sound when the Poke Ball is thrown, and the Poke Ball hovers in mid-air for a bit before falling, plus it takes only one shake instead of the usual three.

There is a small chance critical captures can fail, but most of the time it does land a successful capture. I was happy to see it retained, it was a pretty nice little feature in my opinion.

 

[Psywing]

It occurs both in Gen V and VI. From what I read, it depends on the amount of Pokemon species you have captured. I think Serebii has a page on it with the formula used. You will know when it occurs. When the trainer throws the Pokeball, there is a distinct whooshing/clang sound. This actually happens a lot to me when I encounter a shiny using the PokeRadar. I throw a Quick Ball on the first turn and get a critical capture.

Like Hikamaru said, there is a small chance of this failing.
I also like this feature, it gives me the feeling that the Pokemon wants to come along with me on my journey. :D