Surtr is the second Boss. At the start of the game, take the right path to fight this Boss (if you go left, you will encounter Valravn, God Of Illusion; you will eventually have to fight them both). Surtr is the easiest Boss in the game. He is very slow and does not spawn any minions. Dodge sideways and he will almost always miss you. Then, perform one or two heavy attacks and repeat. Over the course of the fight, Surtr will kneel down and be surrounded by fire. The fire does not hurt you -- so rush towards him and land some heavy attacks from behind while he kneels. This will deplete his health very quickly. If he knocks you on the ground, press X (PlayStation controller) quickly to get back up. When he starts burning, stop attacking and use your vision. This will make him vulnerable and he will stop burning.