Complex sentence: It was not until later that Nintendo decided to distribute Mew through a Nintendo promotional event; however, in 2003 a glitch became widely known, and it could be exploited so anyone could obtain the elusive Pokémon.
Split into simpler sentences: It was not until later that Nintendo decided to distribute Mew through a Nintendo promotional event. However, in 2003 a glitch became widely known, and could be exploited so anyone could obtain the elusive Pokémon.