Hero mode is frustrating. Oh yah, and when I mean right sid of the mountain's zenith I mean by the weird white platform at the top where the Moblin shoot you, on the side of that there's a bomb where you can slide/throw it down the mountain to hit a boulder.
With all modesty, I have beat the game three times including on Hero mode/Hard mode. You should buy this weird recharble thing for your wii remote. Instead of being in agony over batteries. One key is close to the door and the other key is on the right when you slide down the mountain from the section that consists of burning boulders and fire keese. There! Those are the location of the keys.
One key is stuck behind a boulder that can be bombed at the right side of the mountain's zenith, and another is under one of those wooden towers that can be knocked down with a bomb. And then another is in the cave of lava that has to be drained of its contents.