Realtime mesh deformation or texturing

Hi everybody,

I want my special effects to interact with the enviroment. If I shoot a rocket or a magic effect and it its the ground/wall or anything, I want to deform the mesh. Are there any examples for that?

Also I want to do something like decals from bullets. If my magic effect is flying above a surface for example, I want to paint the path black or something (like the magic is burning its way)

Hope I could describe it clearly. Thanks in advance.