Electro Ball depends on how fast you are compared to the target.
>Electro Ball inflicts more damage the faster the user is compared to the target. Therefore, the larger the relative difference between the user's and target's Speed stat, the greater the damage. -Bulbapedia
Unfortunately, this move is only in Black/White and Black 2/White 2.
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This doesn't suit Ninjask at all, but Gyro Ball does more damage the slower you are than the target.
>Gyro Ball inflicts more damage the slower the user is compared to the target. Therefore, the larger the relative difference between the user's and target's Speed stat, the greater the damage. -Bulbapedia
Hope This Helped :D