Here are some links that may help you.

Status Ailments
Critical Hits
Attack explanations
Abilities and info for 2-on-2 battles

The grades for accuracy range from -6 to 0, and the grades for evasion range from -6 to 6. The chance of hitting an opponent with a certain move is calculated as follows:

Base accuracy of the attack × User's accuracy factor / Opponent's evasion factor

The accuracy and evasion factors for each grade are the following:

Grades:	-6	-5	-4	-3	-2	-1	0	1	2	3	4	5	6
Factor:	3/9	3/8	3/7	3/6	3/5	3/4	3/3	4/3	5/3	6/3	7/3	8/3	9/3

As for stat modifications, the grade scale ranges between -6 grades and 6 grades where:

Grades:	-6	-5	-4	-3	-2	-1	0	1	2	3	4	5	6
Factor:	2/8	2/7	2/6	2/5	2/4	2/3	2/2	3/2	4/2	5/2	6/2	7/2	8/2

Just as with accuracy, you multiply the original stat by the factor to get the current stat, and it starts at 0 grades.

I hope that helped.

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