This guy is a royal pain in the @$$! The Oblitergator is much tougher than the other shrine bosses! If you've been following my guides for building powerful armor and weapons, this guy shouldn't give you much issue.
Oblitergator is pretty much the same as the other shrine bosses, you just have to study their attack patterns and the signs for their attacks and you'll do fine. With Oblitergator, DO NOT USE SWORDS OR SPEARS! If you use swords or spears, he will destroy you! Instead, craft the Hell Branch magic staff (again, you only need ONE of each ingredient and you MUST be either close or exactly at the appropriate forging level!). The Hell branch is weaker than the other staffs but it's better for this boss fight because every time you attack with it, the Hell Branch hits your opponent three times in a single attack. Just run along the outside of the ring and wait for an opportunity to attack. BE PATIENT and you'll beat this pain in the neck for a boss!