At vitality level 0, a creature has 100 max hp (hit points). Each additional level in vitality increases max hp by 3%. At prayer level 0, a creature has 100 max pp (prayer points). Each additional level in prayer increases max pp by 3%. So, at vitality level -30, a creature has 41 hp, and at vitality level -60, a creature has 17 hp, and at vitality level 60, a creature has 589 hp, and at vitality level 180, a creature has 20,450 hp. Similar for prayer. A creature with a combat level 24 levels above another is twice as tough as the weaker one (can take down two of the weaker ones).