Terofar

It is extremely difficult boss for paladins and knights due to his skill reducing abilities.

Attacks in melee range.

All vocations: Due to his strong abilities and melee it is advised to use prismatic rings along with Prismatic Necklace, Gill Necklace or Stone Skin Amulets.
Mages: Enter with Energy Ring and Stone Skin Amulet equipped. In the best case scenario, you will summon a monster that will reach Terofar before you do, so he's the one to be inflicted with a curse. If that doesn't work, you should keep an eye on the death hits you get and once it starts hitting over 300, you may want to put an Energy Ring again until the curse is gone. Keep Terofar on diagonal all the time, so you can avoid his waves, keep summoning Fire Devils in case they die, and just shoot it down with your Wand of Defiance/Glacial Rod and Sudden Death Runes. It will take around 10 minutes before it dies even if you are a high level. It's also wise to carry few Mastermind Potions along and drink one of them each time you failed to react fast enough and got yourself hitted with Skill lowering wave.
Paladins: You can start killing it pretty smooth around 400 level. Just stay on diagonal, keep on using Sharpshooter along with Great Spirit Potions and shoot it down with Infernal Bolts, Sudden Death Runes and occasional Strong Ethereal Spear. Remember to heal yourself to full before casting each Sharpshooter. It's also wise to carry Energy Ring and Pot of Blackjack/Rotworm Stew in case things go south and you can't overheal the damage you get.
Knights: It's totally or at least nearly impossible to kill it as a Knight. Better ask your fellow friends with other vocation to do it for you.