I'll take a look at the character pages on the wiki (love the wiki, by the way).
So I guess that if Gruff shows up in Starstill it would have to be fairly early in his character development? The basic plan so far is for him to show up, piss off a dragon and planeswalk away leaving the dragon really, really angry.
How does Gruff go about planeswalking exactly? How would he end up in the middle of a scorching desert? He was just really cold and wanted to warm up?
Gruff's planeswalking is a bit random. Generally, it occurs in similar conditions as Ascending does. As to what planes he ends up, it's also a bit random, since he isn't really aware he's in the Blind Eternities. Seeing that how planeswalker can sorta intuitively sense what a plane is like from the outside, I can see Gruff gravitating toward a warm plane if he was feeling very, very cold.