You can suddenly grow monstrously large (as a 3-shot action). If you use transformation simultaneously, there is no additional shot cost. This costs a Magic point, but also increases your Body greatly; each schtick of Growth gives you a +2 to Body.
Growth usually lasts for a single scene; while grown, you can pay the Magic point again to remain grown for the rest of the session. If you want to be permanently larger, simply get more Body.
Each schtick of Growth gives you 250% mass and 136% length. Your approximate size after Growth can be read on the Body Benchmark Table. Count on the gamemaster to make this a hindrance on occasion.
This has been supplanted by Transformation: Huge.