The second boss in The Legend of Zelda: Skyward Sword occurs at the end of the Earth Temple. The key to this fight is to stay calm, not panic, and remember the safe zone. Immediately the fight instantly ramps up the intensity, as Scaldera will chase Link up the ramp. Scaldera has the ability to launch huge fireballs up the ramp after Link; it also charges after Link in an attempt to step on him.
NOTE: Sources indicate that Scaldera can also bite Link; this did NOT occur during my battle. This boss cannot hurt Link as long as he is standing in the safe zone.
Notice the bomb plants that line the walls of the ramp and top platform; Scaldera itself cannot reach the top of the ramp because the first set of bomb plants explode when it steps on them causing it to roll back down the ramp. The safe zone is located anywhere between the edge of the ramp and one of these bomb plants AFTER the first set.
In order to harm Scaldera, position Link just above the first set of bomb plants (be sure to stay out of range of the explosion that will ensue when Scaldera steps on these) and when Scaldera is hit and starts to roll down the ramp chase after it. Once it hits the bottom, equip a bomb and wait for the animation that signals it is about to inhale then toss a bomb at it. This will cause Scaldera to inhale the bomb and become stunned opening the window for Link to rush in and slash away at his eye.
When Scaldera gets up, it will charge at Link but as long as he puts a decent amount of distance between himself and the boss, the immediate middle of the ramp becomes a safe zone as well, because Scaldera will simply run past Link without causing harm. Once Scaldera hits the first set of bomb plants near the top of the ramp, run to the side and allow the boss to roll safely back down to the bottom and repeat the previous steps to ensure its demise.Skyward Sword - Pyroclastic Fiend Scaldera Boss Guide,