The variables as to a Critical Capture's success includes:
- Number of Pokemon in Pokedex
- Pokemon's Normal Capture Rate
The formula is:
>Critical Capture = floor((255,CatchValue) * Multiplier)
Firstly, 'CatchValue' is simply the normal Catch Value formula, which you can look at in the Generation V section of this page.
Now, if this number is below 255, (hence catchable) then this number is multiplied by a certain value, depending on the amount of species in your Pokedex.
- If <30 Pokemon are in your Pokedex, this value is 0.
- If 31-150 Pokemon are in your Pokedex, this value is 0.5.
- If 151-300 Pokemon are in your Pokedex, this value is 1.
- If 301-450 Pokemon are in your Pokedex, this value is 1.5.
- If 451-600 Pokemon are in your Pokedex, this value is 2.
- If >600 Pokemon are in your Pokedex, this value is 2.5.
So let's say that the 'CatchValue' is 48, and I have 373 Pokemon in my Pokedex.
CatchValue is below 255, so I can continue with the formula. So the formula would be:
48 x 1.5 = 72
Then, a random number (just a random number, not gonna go into unneeded specifics) will be generated, and if the resulting number (in this case, 72) is below that number, a critical capture will occur! :D
Really, the only way to improve the odds is you have to have less Pokemon in your Pokedex. Especially below 30 - since the resulting number will always be 0, and therefore the number will always be below the generated number. Yay. :D
Hope I helped. :)
Source and Above Link.
