I think you've misunderstood something.
A mage cannot turn his magic in coincidental by pretending to be a vampire, because also vampire aren't natural creatures, and people doesn't believe in them.
So magic done with such a pathetic justification, would be raw and crude as if the mage had said nothing, believe me.
To shapechange you need a HUGE amount of dots in Life sphere. It attracts the Paradox and you don't inflict aggravated damage, you don't regenerate and you don't frenzy.
A mage may try to come close to a vampire and a shapeshifter, but he will never be able to use their characteristics at the same level. He should use other ways. Mages tend to be very versatile, and should be clever enough to use this versatility. Oh, well, otherwise they simply die.
The beauty of the WoD is the crossover, besides.
Actually in my Hengeyokai party we're me, a Khan weretiger, and two other guys, a Stargazer Garou and an Akashic Brother mage.
It works pretty well. When we step sideways, the mage simply waits for us on the other side, but besides this, there are no really problems if the Storyteller is skilled enough to know the rules. And ours is

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As far as the dice system goes, it may be uncomfortable to roll 12 dice when you attack, but I think it works pretty well.
Surely better than such a ridiculous concept as armor class, or levels that increase your hit points and the like.
NB: I hate power play, that's why I hate D&D

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I love reading manuals, too. And the ones by White Wolf are the most clear and interesting to read. I have the RPG of Star Wars, which uses the same rules as AD&D, and it took hours to create a character because it was never clear about rules. It's a total chaos

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