here is my simple terrain deformer demo

features are displayed, but you can: raise a vertex closest to the red cube by left click, update terrain hull by U, update hull and set custom normals by F, test terrain hull by a movable character T, move character by WASD, camera is a simple RTS styled one, remove character by pressing T again.

in the main script you can also select loading a wmb instead of created terrain, or not to create water, and also there are some models and map entities which can be created, all by simply uncommenting some lines. but behaviour is the same.