so now we get a Mewtu EVENT (normally only a special stage) and Regigigas - you WANT to bring the other Regi (preferably leveled up) if you want to kill this thing... in Shuffle of course
If that's a "trick" stage (you can only beat it in a certain order or with a certein trick) you can search for it on youtube... I had to a few times (effin' Klingklang)
if you want to train up, use Meowth and try to get at leas a 4-coin row for extra 330 coins per try