How do you get Wario?

I have been playing pretty much the whole game as Yoshi, Mario and Luigi. I have gotten 127 stars as Yoshi, Mario and Luigi, but for some reason I don't know how to get Wario. How do you get Wario? Where is the key to unlock Wario's door, and does anyone else know what is behind the locked door next to Wario's locked door? Also, can anyone tell me what secret stars I am missing? I have talked to All the Toads, Gotten the one in the Wing Cap and Metal Cap Area, I know I am missing the Invisible Cap one, but I can't get that without getting Wario first, since he's really the only one who can pound those big boxes down, and the Invisible Cap entrance is blocked by a big black box. Other one that I have are both stars on Peach's slide, and the little side room after entering the ocean room, Boo's red coins in Peach's backyard. The first and second Bowser level, I am still working on the third one. (I don't know if it is a backyard or not, so I'll just give it that) Those are the only ones I know though. What other secret castle stars am I missing? Also how in the world do you get that secret star in Cool, Cool Mountain it's right below the Birdo's pond, but it's like you can't because it's directly under the ice. I don't think even Wario could do that. I don't know if he could or not, but how in the world do you get that star in Cool, Cool Mountain? Has anyone done it. If so, can you tell me how to get that star as well? Any information would be helpful to me. Thanks.