Stardusk the LV6 female Ponyta vs. Nightmare the LV7 male Meowth

Miko vs. Link10

Stardusk
HP 25
Attack 18
Defense 15
Speed 19
Special Attack 16
Special Defense 16

Nightmare
HP 27
Attack 15
Defense 14
Speed 22
Special Attack 15
Special Defense 15

Nightmare's Slash began the battle. Stardusk took 8 damage.
Stardusk retaliated with Overheat, which caused 17 damage. Her Special Attack fell two grades.

Nightmare: HP 10
Stardusk: HP 17, Special Attack 8

Nightmare Slashed again, this time hitting a weak spot. It's a Critical Hit! It caused 14 damage.
Stardusk repeated her Overheat. Despite her Special Attack cut she dealt 9 damage. Her Special Attack fell another two grades.

Nightmare: HP 1
Stardusk: HP 3, Special Attack 5

Nightmare's final Slash finished Stardusk off.

Nightmare: HP 1
Stardusk: FNT

Close battle. Like in RBY, these battles tend to boil down to luck and speed.