How do you get the legendary treasure in perilous pastures for skylanders?

some people say you need an earth skylander but you can do it with drill sergeant but he may need to be fully upgraded and mabye some other skylanders might work BUT DO NOT I REPEAT DO NET USE CHOP CHOP HE CANT TAKDOWN THE ROKES. How you get to the treasure is you get to the magic eliment and on the the bottom floor of to the side is some stairs that if you go down and look you will find it.