Leliana will kill him easy actually. Get a powerful bow, run around a few times and he'll pull out his crossbow (which sucks)
(use a bow with rapid aim)
1. pinning shot
2. shattering shot
3. crippling shot
4. critical shot
5. restore stamina
6. shattering shot
7. arrow of slaying (possible a 150 damage hit, even on nightmare.
8. Fereldan's hero just got pwned by a girl, and to rub salt on the wound, she's an Orlesian. Loghain doesn't have any special ability with range attacks, and he misses A LOT. Zevran died with 4 hits without a chance to restore health. Alistar didn't stand a chance, Sten didn't even land a hit, Ogren got beat down (if thats possible), Morrigan's entropy spells held him off a little.... but got kill within the next second paralyze wore off. Shale was stuck between a rock and a hard place, and of course, my level 20 arcane warrior/blood mage who has over 400hp, and Warden Commander Set fought like this.
1. Crushing prison
2.blood wound
3. Bloody grasp
4. fought a little taking only 3 damage per hit with shimmering shield
5. crushing prison again
6. blood wound again
7. Virulent walking bomb... to bad he didn't explode. My health bar was tiny, thats how much powerful magic power it takes to kill Loghain on nightmare, when you only need (i had blood mage ring so spells take .6x of health to cast) .6*(cost*1.72) the 1.72 is the fatigue (72%).
Unless loghain has 200 defense, i think theres a bug, my level 20 Berserker/champion with 112 attack dual wielding can barely land a hit on loghain, and I have 130 defense and he's landing hits like crazy. I mean CMON! I soloed Flemeth and can't kill Loghain??!!! WTF