Simplify the following text for a Grade 6 native English-speaking person.
Original: In Japan Super Mario Galaxy 2 sold 143,000 copies on its first day of release and 340,000 copies in its first week , about 90,000 more than the first Super Mario Galaxy sold in the same amount of time .
Simplified: Super Mario Galaxy 2 is a video game for the Wii . It is the sequel to Super Mario Galaxy .