The Monster Manual 2 gives us the Titanic template. This is a template that can be added to any medium or smaller animal or vermin. Among other things, it increases their size to Gargantuan.
The book states the following regarding the origin of such beasts:
Titanic creatures are the result of powerful transformation magic as well as forces of nature gone awry.
Hence, my question: What kind of magic? What could a player (Or NPC) do to actually create a Titanic creature?