The name Mafalda is a girl's name of Italian, Portuguese origin. Mafalda and is often added to lists like Girl Names Uncommon in the US and discussed in our forums with posts like "Heaven, Hell, or Purgatory- Harry Potter".
From the experts:
Mafalda is nearly unknown in the English-speaking world, despite an appearance in Harry Potter. Indeed, it does have a witchy feel. Matilda itself is preferable, or her French form Mathilde, Spanish Matilde, or abbreviation Maud.