I have played the Windspear hills alot of times and when killing the big red you-know-what I feel like I want to get Garren Windspear back in power of the land. He has only suffered and I think he needs to be cheered up! I have never found a way to restore him lord of the land, but I heard you can do it somewhere. is this totally wrong or can I do it somehow?

I've never heard of such a thing, not even as a mod. Personally, I think he's happy as he is--he's got his kid back, he owns a big house....the Ankhegs in the front yard are a bit pesky, but he can live with that.

He doesn't redeem his land after you kill big f and complete his quest?

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Isn't that the paladin stronghold quest?

I just browsed Shadowkeeper and there is a scroll that is like the deed of the windspear hills. I remember it because it was persicely what I wanted to do!

Yeah, but...
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You get that if you kill Garren on behalf of Firkragg.