Well, PC Starman was able to gain PC Kryptonain stats from what I remeber. This is the same dude, just without the stats. He was able to sink an island with ease as well and create black holes, like you said. He makes things heavier and I can't see Sinestro working around that.
While gravity can be tricky, rings have a lot of power to break free from even extreme gravity, and Sinestro has the firepower to take him out while he's trying to use that gravity, the big problem.
It's been a long time since he had kryptonian powers.
Yeah, he draws mass from stars and places it in any object. Can be tricky for Sinestro or any Corps member. He doesn't manipulate gravity per se, but he can increase Sinestro's body a thousand fold and what will he do then?
He's also sank Atlantis, he's manipulated people who fly, so they wouldn't be carried away by space-vortexes, and even manipulate weightless objects.
How would increasing Sinestro's mass stop him from fighting, though?
Doing that often pins other enemies to the ground (if not crushes them), but the ring works on will, so even if he's massive and can't really move, he can fire energy bolts.
Good point, but he can also manipulate objects. Maybe he can do the same to Sinestro's ring and confuse Sinestro while he's manipulating his body. Sinestro will have to fight for it.