We all know HE'S the star...who's this Mario of which you speak?
Your character SHOULD be on a keychain or keyring or something of the sort. The first step is to carefully break that off (Save it! You can always recycle it and make a keychain!). After this, put a Jump Ring through the eyelet that should be left on the top.
Prepare your necklace. Make it the length you like. Attach Yoshi to the chain, but not through the holes. He should be able to slide around on the chain. Close the ends of your necklace chain.
Select your beads. This is the hard-ish part. Get a head pin and add (in this order) glass seed bead, large wooden bead, small wooden bead, large wooden bead, glass seed bead. After that, use your needle nose pliers to curl the remainder of the pin. Attach a jump ring through this hoop. Attach this string onto the jump ring by Yoshi's head.
Pick up your two star buttons. Place the flat side to flat side, making sure the holes in the buttons line up. Put a jump ring through one of the holes. Attach this little number to a length of chain. On the other end of the chain, attach it to the jump ring by Yoshi's head. Vwah la! That's it!