In the Jedi Academy game there is a sand monster that is just like the bolded idea you had Bingo. It only pops up when you are on the sand. The only cover is jumping on rocks. So I could imagine something like that. I would love to see it anticipating Lando. Instead of tentacling him to it's mouth it could be squirming closer to him.
There is the gargantuan. But it doesn't necessarily have to come out of the sand. Unless we could add a dramatic effect of it coming out at nearly the last minute right when Lando is just about to get out of the sand though that might be too much. The monster is called a sand burrower. I like the way the mouth is. To me it is basically the sarlacc that never was.
