Step on the switch to activate the final moving pathway.  This takes you to a showdown with the boss.

There’s nowhere to hide, so when the boss comes out of the lava you need to shoot it before it cooks you.

The boss attacks three times, using increasingly elaborate decoys.  There are no tricks to fighting it.  You just need to be fast.

When the boss is finally defeated, the moving pathway will take you to the treasure.