To unlock this trophy you need to cast Tarantallegra on any character and the easiest place to do so is in the Hogwarts Hub.
After unlocking Draco Malfoy, you'll want to go to the cauldron and select Draco as your playable character. Once you are Malfoy, you'll need to select the 'red' spell, which is defaulted to show Immobilus. Press and hold the
button and change the 'red' spell to Tarantallegra by using the
button needs to be held down to change to this spell. All that is left to do is target another character in the hub (using the
button again) and fire.