I'd build up the musculature on the chest and thighs in particular, those bulk up the figure in general as its head - whilst monstrous -, makes it appear a bit top heavy. A set of pointed, or cauliflower ears would balance out the head a bit more too.
If you're leaving it nude then perhaps over emphasize veins and muscles in places. Like on a body builder who's done too many steroids. To make it grotesque. Conversely giving it flabby skins and a distended stomach would contrast this and how animated the pose is- again making it look as ghastly as possible. Open soars, and dry skin may be a bit much.
I'd leave it bald. A shock of hair about the shoulders or on the chest may be an option, but I think it'd look better hairless.
With the tentacles if you're going for the exposed tendon look maybe add some areas where it looks like the "skins" been torn, with a different texture underneath. Or the odd scale, or row of teeth in a place where they shouldn't be. Something to set them further apart from the main body of the figure. I assume you want to add teeth to the ends of the tentacles. Long tongues could work too - with sculpted on saliva dripping from them?
As for the overall form of the model. Having it bumpy and malformed is fine. Maybe even add bumps where there shouldn't, as tumorous growths.
If you do want to add armour or cloth then I'd keep it light. The remains of a torn loincloth or scraps of armour held on by belts, or bolted onto stretched skin. Perhaps a chain hanging loosely around a thigh.
Overall my angle's to go towards something like a Flesh Atronach from the Elder Scrolls series, but that's just my take. You could go a completely different way. The one below's my sculpt inspired by that look.