Probability script?

Scripting
1

I want to make random magic effect something like critical hit.

So I need chance scripting.

Please let me know some idea or concept or script tip or itself.

2

Random
Class for generating random data.

Class Variables
seed: Sets the seed for the random number generator.
value: Returns a random number between 0.0 [inclusive] and 1.0 [inclusive] (Read Only).