Overview
Seto was the chief of his tribe of bestial guardians, watching over Cosmo Canyon. He single-handedly fought off an invasion of the rival Gi Tribe, sacrificing himself to stand vigil over a side entrance of the canyon. Over decades the curse has faded, and technomagical remedies have helped him "thaw" a little bit and lead some semblance of a normal life. Though still hewn of stone, he can at least move and speak again. By turns a jolly giant or the regal, stoic chieftain, Seto has risen to answer as the Planet cries out for help once more. He's taken reluctant leave of his family and his people to explore the World Tree for answers.
Perks
Art of Camouflage: In rocky terrain, stone-bodied Seto can hide in plain sight.
Having a body made of rock means it's easy for him to hide in... well... rock. When he hunkers down and remains preternaturally still, Seto can virtually disappear. Best of all, he doesn't have a heat signature to follow! A weird beast sculpture in the middle of the scenery might be a little suspicious in some places, though...
Cosmo Canyon: Seto has a home base where he can patch himself up.
As the chieftain of the beast tribe that protects Cosmo Canyon, Seto always has a home to return to. A rugged desert canyon sparsely populated by humans and what few guardians remain, it's hot in the day and frigid at night. The region is easily defensible with its labyrinthine canyons, rough trails, and high mesa plateaus; Seto knows the terrain like the back of his petrified paw. It's here that he can always return to for rest, or if his stone body has been broken and needs mending.
Cry of the Planet: Seto can sense corruption and wrongness; the inversion of natural order.
All of Seto's species are alert to changes in the Lifestream, the spirit-energy surrounding the Planet. Through this they can sense the Planet's pain, to varying degrees. Pinpointing the problem might be harder, but Seto knows without a doubt if something isn't right with his world. To a lesser extent, he can sense the pain of other worlds, though this is much less reliable: It can hit him like a ton of bricks stapled to a migraine, or he can be wholly oblivious to a given world's suffering. (Consent required for worlds not his own.)
Great Warrior: A fierce warrior-chieftain, Seto can use the whole of his body as a weapon.
Seto is a seasoned warrior and chieftain of his tribe. He's a tremendously skilled fighter, having sharpened his claws on the rival Gi tribe, and knows how to use his body to every advantage. In battle he relies on his natural weapons of teeth, claws, and bulk. More than that, he's learned how to adapt to battle with his stony hide. His claws are still razor sharp and stronger than they ever were. His fangs are like spikes of diamond. The broken spear-hafts jutting from his torso can impale things, if he's crafty about it. He's slower than he was, but he can still try to overpower and overwhelm foes, bearing down on them like a boulder and using the crushing force of his own mass.
Physical Quirks: Seto's stone body has a reduced metabolism and few needs to tend to.
Seto's stone body has its perks. He can breathe, sleep, and eat or drink, but he doesn't strictly need to do any of those things. His sense of touch is so deadened that he can only feel slight changes in temperature. He also cannot feel pain, although that is dangerous as much as it is advantageous. All of these together can be a potential help when exploring environments hostile to life.
Strength of the Earth: Most of Seto's body is as strong and resilient as stone.
Having been petrified and later partly "thawed" through a combination of magic and technology, Seto's body remains as resilient and tough as stone. He is tremendously strong, able to leverage his strength and density to literally throw around his weight. He's also quite large in addition to being disproportionately heavy; enough so that it might take real effort to physically move or intimidate him... and never mind toppling him!
Complications
Ablative Body: Seto inconveniently loses the use of any stone pieces that break off of him.
With a deadened sense of pain, Seto is sometimes unaware of damage done to his body. When he loses pieces in battle or through accidental means, he will immediately lose the use of that piece. A skilled healer or magician can reattach them, but he has to find a way to save those pieces and transport them to the one to do the mending. Save the pieces...! (The specifics are left vague so PC healers are able to jump in and use their skills.)
Bones of the Earth: Seto is dangerously stone-heavy, and can unwittingly break things.
The curse of petrification has made Seto's body tremendously heavy. He doesn't necessarily know his own strength or weight, and he has an unfortunate habit of unwittingly breaking things. He has to tread cautiously over artificial flooring, testing them before he puts his weight down on a structure that may or may not be able to support him. Touching furniture is right out of the question. His sense of touch is also deadened, so he doesn't always realise his proximity to things more fragile than he.
Flame Tail: Seto's tail is a potential accidental fire hazard.
Like all of his kind, the end of Seto's tail hosts a flame. In his case, it's a guttering blue thing that scarcely burns, but it's still there. With his deadened sense of touch and habit of standing very still, Seto can accidentally set fire to flammable thing if he leaves it up against anything that can burn for too long. His sense of smell is also deadened, so he may not necessarily smell anything burning! Furthermore, the flame on his tail can be extinguished. It'll reignite itself a little while later, but the sensation is awkward and uncomfortable one for him.
Sink Like A...: With a body of rock, Seto also sinks like a rock.
With such crushing physical weight, it comes as no surprise that Seto has no buoyancy in water. Nope. He'll go straight to the bottom. The fact that he doesn't need to breathe is a plus, but it can still be massively inconvenient for him, and maybe give any allies or friends that don't know his quirks a scare. He can only move slowly in water, so he may fall behind allies in aquatic places.
The Immovable Object: Seto can be stubborn, and his pride easily wounded.
As a chieftain and an established warrior, Seto can be very set in his ways, and a hidebound traditionalist. When he puts his mind to something it can take tremendous effort to change it. That's not to say that he can't be convinced of a more correct course of action, but it better be logical. Following that vein, his warrior's pride can be stung easily, and he can be spiky as a gravel bed if he perceives a slight.
Wrath of Winter: Ice can deal brutal damage to Seto's stone body, and he is wary of it.
Seto must be very careful around sources of extreme cold, or moisture that might condense and freeze. Ice can open up great cracks in his stony hide, and while he might not feel the pain of it, it can still deal devastating damage to his body. He doesn't like ice, ice magic, or magicians who heavily use ice; being naturally wary of them, and will always have a certain degree of unease around them. The sight of a whole bunch of ice can strike fear into him as much as the sight of a roaring bonfire to a pyrophobe.