Saruman: I am the train that runs over said person.

Gandalf: I am the broken track that derails the train!

Saruman: I am the team of workmen that fixes the track.

Gandalf: I am the really bad techinque used by the workmen that causes the tracks to break again.

Saruman: I'm your average superhero who carries the train over the broken bit.

http://i75.photobucket.com/albums/i2...ah/Gandalf.jpg : I am the annoying man who sues the Super hero.

Saurman: Well... I am the super hero that goes out in disguise, so the annoying man doesn't know it is me!!!!!!!!

Gandalf: Well i am the annoying fan that recognizes you, that then alerts the annoying man who sues you.

Saruman: I am the Dragon that eats the fan. So there! Two can play at this game!

I'm glad this got revived!
 

http://i75.photobucket.com/albums/i2...ah/Gandalf.jpg: I am the arrow bloke who shoots the Dragon in the face repeatedly. :p

Saruman: I am the wind that blows the arrow off course.

Gandalf: I am the same wind, which also blows out the dragon's fire.

Saruman: I am still that same wind, which fans the brushfire started by the dragon.

Gandalf: I am the fireman who puts out the blaze.

Saruman: I am the holes in the hose that prevent good water pressure.

http://i75.photobucket.com/albums/i2...ah/Gandalf.jpg: I am the water-vomiting enormous beast which is not feeling too well and puts out the fire by accident.

What? They exist in the Legendarium! They're on... page 781... of the... 7th book.

I am the lightning bolt that strikes the watery abomination.

Gandalf: I am the Vala that saved the monster.

http://i75.photobucket.com/albums/i2...ah/Saruman.jpg: I am the sudden onset of scurvy that stops the Vala from helping.

Gandalf: I am the lime that the Vala ate to get rid of the scurvy.

Saruman: I am the cyanide that was in the lime.

Gandalf: I am the involuntary reflex that made the Vala spit it out.

http://i75.photobucket.com/albums/i2...ah/Saruman.jpg : I am the angry (and inexplicably magical) dog the Valar were sick on which then turns and attacks them.