Undead slayer badges are one of the most useful resources in the game (just under defender's medals and PvP trophies). You can use them to train 3 armors (paladin, necromancer, and deathknight) and you can use them to purify doom weapons and to upgrade destiny weapons. what most people don't know is that the easiest way to get them is to go to the necropolis, talk to artix, click on quests, and to click "save moonridge" (not the next one "moonridge saved!"). This is a link back to the war that happened at the beginning of the zone, but instead of the reward being defender's medals, you get undead slayer badges. the waves range from 1-7 monsters per wave, and the badge is a 100% drop. be sure to have a good fire and light weapon (or at least just have a light weapon) because all the monsters are weak against light (except for necroslimes, weak against fire). Beware of the skelemancers, they hit very hard. I'm lvl 36 and they hit me like 200-300 energy.