Jotun Feast-Caller is one of my favourites, and set 4 made the decks that like it better (in my view).
The Shadow splash is something I'm testing at the moment. I find that Hooru control-style decks are really lacking in lifegain, and
Black-Sky Harbinger is so good at stabilizing you that I feel it's worth the splash. The only other card I found worth splashing is a removal catch-all in the form of
Slay. The removal suite is highly customizable, and I'm thinking of trying
Lightning Strike, or a split between
Slay and
Vanquish.
The deck has been testing relatively well, although I'm not sure it's the best home for the Jotun. I can see myself cutting him, since he conflicts with
Harsh Rule on 5, or finding a better win condition that has evasion from ground creatures.
In my experience, Feast-Caller performs best in decks that are lower to the ground than this one, so it's likely there's a better home for him out there. Regardless, I think Hooru Control is, as of yet, under-explored in the set 4 metagame.