After you defeat the mini-Boss the second time (use Axl and Zero with Palette as navigator), Palette tells you that there is an ice path on the top pf the ledge. Go up there with Zero, then use Axl to hover over to the left to get the Rare Metal. Go back to that stage with X and Zero. After defeating the mini-Boss the second time go back up the ledge (before going to Avalanche Yeti) with Zero. Melt the ice with either weapon obtained from Optic Sunflower, then switch to X to get the Helmet H armor piece.
