Board Thread:Questions and Answers/@comment-23873172-20140721165330/@comment-4536066-20140721190609

If you wanted, you could treat it like any other variety of magic: the more practice a character has at doing the task, the faster and easier he will be able to complete that task successfully. A brand new wizard who has barely touched magic will struggle his first time just to maintain a candle flame, whereas an archmage who has been practicing for five decades might be able to safely produce a huge ball of molten fire in just a matter of moments. Translates to shapeshifting pretty directly.