Hello all,
Finished this fight Sunday night on Hard difficulty, two-shot it with a party of 4 at 4th level. Since I like to play these games with a mild degree of immersion, I didn't utilize any positioning tricks. It's difficult but doable at this level even with the initial charge and being vastly outnumbered. Thought I would post some tips regarding what to do. My party: Me (4th level Druid), Eder, Aloth, Durance. Tips, in no particular order.
1. Focus on disabling spells over blasts to start: This is a key rule in all Infinity Engine-style games. Going pew-pew-pew will only get you to the reload screen, fast. Open with spells that will take several enemies temporarily out of the fight, either knocking them prone (Slicken, Repulsing Seal), or confuse them (Bewildering Spectacle). Confusion is great because it causes your enemies to fight amongst themselves and soften each other up for you.
2. Use self-buffs, consumables and HoT (heal-over-time): Potions can only be used in-combat . . . but food buffs can be gained anytime and stack with potions. Take advantage of this as things like Savory Pies and Ricepans are easy to craft or just buy from the Black Hound. During the fight, make sure Durance or your pocket-priest pops Holy Radiance as the first or second action to keep everyone's Endurance up. Crafting/buying potions of Power (for your tanks) or Minor Regeneration and using them halfway through the fight can make sure that at least one member of your party is left standing. Also, make sure that you have at least a couple of scrolls of Restore Minor/Light Endurance in the Quickbar of a high-Lore character as these are relatively easy to craft and can heal multiple characters quickly as long as you are all stacked up.
3. Kill/neutralize the mages first: Basic rule in any D&D-style game. The archmages need to be focus-fired down fast before they destroy you. Use a ranged attacker with high damage (Kana is ideal if you have him) and a spell like Fetid Caress to take them down, or make sure they are included in the AoE of your disabling spells and prioritize them for your high damage dealers.
4. Debuff Raedric: He has a nasty two-handed blade and can take down your tank in 3-4 swipes if he crits. Blind him, frighten him, charm him . . . just don't let him hack away at you (I learned this the hard way when he dropped my druid in werewolf form).
5. Bypass DR when it's time to blast: Raedric and all his bodyguards/champions are plate wearers. . . . and plate has a DR of 6 against Shock damage. Spam electrical attacks (Jolting Touch/Dancing Bolts) if you have access to these spells, and remember that a wizard's Arcane Assault is Raw damage (bypasses all DR).
Hope this helps! Remember, it's a challenging fight (especially at lower player or higher difficulty levels) and all the more satisfying to beat because of this. Enjoy looting his Keep after.