Simplify the following text for a Grade 9 native English-speaking person.
Original: Unlike other characters in the PokÃ mon franchise , Mew 's development was not overseen by Ken Sugimori , but by Game Freak programmer Shigeki Morimoto . Morimoto programmed Mew into the game secretly , as a prank amongst the staff just prior to its release in Japan , intending it to be a PokÃ mon only Game Freak staff members would know about and be able to obtain .
Simplified: Mew was secretly put in the game by one of the lead programmers , Shigeki Morimoto .