Deus ex machina

Deus Ex Machina is a term for when a plot device in which a surprising or unexpected event occurs in a story's plot, often to resolve flaws or tie up loose ends in the narrative.

When used in Transformers, It's mainly a new character coming out of no where and kicking everyones ass (New toy). Or when a dead character comes back for some reason, or gets a  New body (again, new toy). Sometimes however it's just Conveniently  used  accesories.