Just an FYI: Ambient Mana is free for anyone to use, it isn't like Mana purified by the Core, which marks the Mana used with your 'signature' and thus making it truly yours. Ambient Mana can be used like normal Mana from the Core; but it can and will damage the caster, since not all of the spell is marked. But it can be used to fill in spells, thus using less Mana from the Core. Doing this is slower than using Core Mana, however, as you'll have to will the surrounding mana, if there's enough there for the spell anyway, shape it then it becomes whatever you spell you wanted to cast.