Complex sentence: After receiving the electric type Pokémon, Pikachu as a starter Pokémon from Professor Oak because he woke up late, and all the other starter Pokémon were taken, Ash left Pallet Town to start his journey.
Split into simpler sentences: After receiving the electric type Pokémon, Pikachu as a starter Pokémon from Professor Oak because he woke up late. All the other starter Pokémon were taken, Ash left Pallet Town to start his journey.