I was working the other day on trying to make a shapeshifter that could actually compete with metahuman characters when I had an odd notion.
Can a shapeshifter sustain a spell while shapechanging? After all, shapeshifting is not an exclusive action. And what if the Shapeshifter uses a sustaining foci?
With most spells this isn't a problem. Nobody's going to have a problem with a shapeshifter who changes form while sustaining a "Detect Enemies" spell. But there's at least one area that could be prone to heavy abuse here.
Shapeshifters can use sorcery in their animal or human form. So combine that with improve attribute/initiative spells. Now imagine a Tiger Shapeshifter.
Mr. Tiger gets insane initiative in tiger form. He's got +2 initiative die and +1 reaction. Let's assume Mr. Tiger has Intelligence 6. In tiger form he has Quickness 8. In human form? Quickness 1. That means that his reaction, the TN for an improve reaction/initiative spell, is only 3. It's easy for him to get six successes and have his reaction at 9 in human form.
Now, while sustaining the Improved Reaction and Initiative spells, he shapeshifts. In animal form he has Reaction 8. Plus six gives him reaction 14. His initiative is now 14 + 6d6, making even MBW4 look slow. And forget spells, he's put his magic on spell defense because his melee combat skill in animal form is reaction, so he's throwing 14 die and can probably take even a maxed-out melee combat adept without a big problem, particularly when you consider the bonuses to unarmed damage Tigers have. . .
And things get even worse if Mr. Tiger has a bit of experience and bonds himself a nice sustaining Foci or two. Now he cast's improve Quickness on himself with a TN of 2. . .
The thing is, I'm not sure this is really such a doomsday scenario. Shapeshifters are way too gimped as it is and they need a few super-assets to power themselves up to match metahumans.