Kraidgief has 15 hit points at the start, so when you hit him 15 times, he goes to his next phase. UNLESS you hit him many times again, then he will skip all of his phases and go directly to the last phase. Oh, and BTW, you can simply press "Q" while going down his hole to achieve invincibility. You will have to restart the application afterward, unless you want that annoying GAME OVER sign to travel with you everywhere
