In the mountain stage, there are TONS of boxes of items and metatron,
you can get all the boxes(which have about 3 types of ammo in each)
leave then come back to the stage and get them all over again!

You also get the bounder side arm here too. You go towards the dam when
you first enter the stage(it's to the left) and there will be a red box
with the pass code at the bottom of the dam. then at the top and to the
right, when your facing the dam, there's the driver.

BUT there are many enemies here, and they're not marked on the map
either...If it weren't for the all the metatron all over...It would be a
pretty hard stage. They show up at about every other box or so.