Magic Mountain is closing Colossus in August. It's running backwards for the next two weeks, and then forwards until August. Then it will be closed.
Colossus is a classic wooden roller coaster and one of the best rides in the park, though it is a bit rough these days. I have lots of memories of this ride.
If you want to ride it for one last time/your first time, better do it soon. (also, if you've never ridden it backwards, YOU NEED TO GO TO MM. Like, right now)