Breaking the Weave

As you cast this spell, you call upon Mystra and her power, and as you do, you see everything vanish that is used for this spell. As you call upon her power you begin to feel nauseous, and take 2d6 Physic Damage. But eventually, at the end of the spell roll a DC 17 Int Save Check, on Success you unlock something inside you, as if new spells had appeared. In your campaign if your DM allows, you have unlocked 10th Level Spells. On a fail of the Int Save Check, you begin to feel... as if you can't cast that many high spells, you go down 2 Levels.

And if you try to cast a 10th Level Spell, you would have a 25% Chance of Successfully casting it, and as you cast it a second time a 50% Chance.