AUS GBA version if i have time.

Understand how stat-changing moves like Growl and Double Team work in Pokémon Diamond and Pearl. Learn about the 10% per level increase/decrease and accuracy/evasion calculations.

Q: How much do stat-changing moves (like Growl, Withdraw, Sword Dance) increase or decrease stats per "level"?

A: In Pokémon Diamond and Pearl, stat changes are often described in "levels." Each level represents a 10% change to a specific stat. For example, Growl decreases the opponent's Attack by one level (10%).

When a stat is increased or decreased, it's a percentage of the Pokémon's base stat for that category. If a Pokémon's Evasion is raised by 5 levels (50%), its Evasion becomes 150% of its base. If an opponent's Accuracy is lowered by 50%, their moves will hit with 50% of their original accuracy.

ScizorsIronFist adds clarification on calculations:

The calculation for accuracy and evasion is multiplicative, not subtractive. If a Pokémon has 50% increased Evasion and an opponent has 50% reduced Accuracy, the effective accuracy of the opponent's attacks is calculated as follows:

Original Accuracy x (1 - Opponent's Accuracy Reduction) x (1 + User's Evasion Increase)

For example, if an opponent's accuracy is reduced by 50% (meaning they hit with 50% of their normal accuracy) and your Pokémon's evasion is boosted by 50% (meaning they are harder to hit by 50%), the effective accuracy of the opponent's attacks is:

100% x (1 - 0.50) x (1 + 0.50) = 100% x 0.50 x 1.50 = 75%

This means the opponent's attacks will only hit 75% of the time. The description of stat changes as a percentage is a way to understand hidden mechanics, as the game doesn't explicitly state these values.