You get it when you recruit Ho-oh though I am not sure if you have to recruit it or just beat it
Western Cave
he's in western cave
Keys can be found on the floor in Solar Cave and Western Cave. They are more frequently found in Solar Cave, though.
99 and at the end is mewtwo
Western cave
In solar cave
recruit ho oh
it's the same as the pokemon mystery dungeon red rescue team. you can find mewtwo in the western cave once you recruited ho-oh.
Mewtwo is level 99 of western cave his friends area is cryptic cave be expecting strong Pokemon in western cave
Mystery dungeon blue:- At the end of western cave. 99f western cave. Must have friend area.
There are several deungeons you can get it. You can get him in wish cave and western cave.
Yes, there is alot! such as, Western Cave Purity Forest Deep Sea Cave Silver Trench and many more!!!