The Transformation Spell is a basic Metamorphosis Magic spell which is used to convert a person or creature into in the mental image that the user forms. To use it, the user must form a clear mental image or else the spell will fail. Usually used to transform the target into animals, it can also be used to take the form of a specific individual.
This is a very versatile spell and is Akko's most used spell by far.
Professor Badcock had the students demonstrate proficiency with this spell at the beginning of the episode. While all the students could do it correctly to transform a mouse into different animals, in the case of Lotte a capybara, Sucy a bat and Diana a white horse, Akko ends up accidentally giving herself animal traits.
Akko, Lotte and Sucy use this spell in the episode to turn themselves into fish and find Professor Pisces more easily. Akko was not able to become completely into a fish, instead becoming a merman, but she is able to breathe underwater and speak to fish. After this experience she can understand fish language.
Akko uses this spell to transform a normal squirrel into a giant monster squirrel to distract the bouncers at Andrew's party and sneak in during the commotion.
Akko is continuing early morning practice of this spell with Ursula. She makes some advances by transforming herself into a monkey with rabbit ears and a flying elephant.
Akko continues training with this spell for three weeks and three days for her performance in the Samhain Festival. She transforms into a mouse perfectly and still cannot keep aloft for long as a flying elephant, but Sucy and Lotte are there to support her. She later casts the metamorphasis spell with results similar to Arae Aryrha, that is she can transform between semi-tangible glowing animals that can fly despite their anatomy. She can never get this quite right, but gets laughs from the audience, which is what counts.
Akko uses this spell to transform herself into a mouse again to infiltrate Appleton Academy with Amanda.
Akko has mastered the spell at this point. She uses it to become a mouse and escape the cage in which Constanze had trapped her. Later she uses it again to become a penguin and escape the monk chasing her.
Akko uses this spell masterfully to save Diana from Daryl's snakes. First she becomes a mouse to cross a bridge of plants, then a bird to evade the attack of the snake that held Diana and an elephant to crush it. Akko finally transforms into a giant tortoise to protect herself from the bites of the snakes.
Akko uses this spell to transform the missiles projected from the Noir Rod into different bright animals. Also to transform itself into mouse and tortoise to avoid the danger.