My brother was recently playing on the game looking for greenstas when he came across a little glitch on World 4 - Super Massive Galaxy! On it you come to a part where there are 3 koopa troopers crawling around a small cricular world. If you jump onto one of there shells and keep jumping it make a note that gets higher and higher! Afte about 3-5 jumps every jump you land on the shell (In a combo) You get a 1-up! My brother now has 99 xD
Hope I helped!
Hope I helped!