I'm going to assume you already have the Yoshi egg from the hotdog stall. Fight the Iron Clefts and run away, then go back to the locker room. Yoshi will be hatched by now. Name him and fight the Iron Clefts again with Yoshi as your partner. Use his Gulp attack to beat them.
10000 posts at last! w00t! Okay, I'm off into a quiet retirement. Don't bother me.