Everything

Typically, the attacker and defender keep a single Sphere as the Gladius and another as the Aegis. A tricky mage, how­ ever, might shift between them in mid-duel, replacing one for the other. She could even pull one of her reserve spheres into play, changing tactics by switching spheres.

In game terms, it takes one turn to transform the Gladius into the Aegis, the Aegis into the Gladius, or a reserve sphere into either the weapon or the shield. Under most circumstances, there’s no roll required – the ability to switch between spheres easily is built into the circle. Under extreme circumstances (injury, fury, fear, etc.), the duelist might have to roll her Willpower against difficulty 7 in order to change them in the middle of a match. A successful roll allows her to do so easily, and a failed roll reflects scrambled concentration. That failed roll allows the opponent to get one free attack while the duelist regains her composure. After that, she can try to switch the spheres again, though at the usual penalty for a new attempt at a failed roll. (See Trying it Again in Mage 20, pps. 392-393.)