Towards the end of Act 1 Level 5 you will fight the Mossback Stomper, a large tree monster. 1st phase you damage his hands. After that he will pound the ground and rocks fall from the sky. You can hide behind these to protect you from his ray attack. When his head drops to the ground, you can damage him. He will pound the ground and rocks will fall again. This cyle repeats until you wittle his health down enough to beat him. You should be able to beat this boss quite easliy.
If you get low on health you can defeat the enemies that spawn between attacks (they drop food, but not always) or use a health potion (press up on d-pad).