Best way to make irregular terrain?

I'd like to make irregular (e.g. rocky) terrain. What would be the best way to achieve it?

I think it is best to use minimal actors and the polygonal terrain tool, but I didn't find a way to edit the shape of the terrain in the scene editor (say, if I want to add a rock). It would be great to be able to add or move vertices.

But if terrain really is the best option, then I'll just delete and redraw every shape I want to modify, it's not a big deal.

As far as I can see,  there is not a way to edit a terrain.

As an alternative to actors, you could also use a foreground (although it would be more difficult to adjust it)