Ash beats the mauville city gym in three moves. With his pikachu (which is not very effective )against all his electric Pokemon why?
The reason for this is that Pikachu had been supercharged with electricity earlier in the episode. Really, this is just anime logic at work.
1; Pikachu may have been using Dig or another SE move
2; Pikachu might have been on a level WAY higher than the Gym leaders Pokemon.