Vigil would be a better choice, both in general for soloing since you have less resolve and enemies have less armor (= you do more damage) so it almost always outheals DoC, and in this specific case because horridon takes tons of extra damage. That spell does still exist
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For the drakarri adds, 2 tips: 1, use savage defense. They're so low level that it'll take you to 90+% dodge/miss, in fact I wouldn't be surprised if it's 100% now with better gear + agi trinkets. They don't apply the DoT on whiffed attacks. 2, use FoN. They don't taunt or hold threat or anything, but the adds focus on random enemies and that gives them something else to focus on.