Many video games have had a "big head mode". But who calls it "big head mode"? Not Harry Potter. In his next game, he inflates craniums with a spell called "Engorgio Skullus!"
Other spells appearing in the DS version of Lego Harry Potter: Years 1-4 include Vomitare Viridis (which makes the average Hogwarts student upchuck Lego bricks) and Melofors (which turns a Lego person's head into a pumpkin.) Use these spells to zap other characters and change them in the June Potter game.
The game and its console big brother have more useful spells that can be cast by Harry and others. In the DS version I saw Reducto and Repairo, Leviosa and Incendio, all good classic spells that can be used to shoot, build, levitate or burn things. J.K. Rowling would approve. In fact, she did. The Potter author wrote many of those spells in her novels that inspired the Potter games we can now play. Those that weren't in the books were at least approved by Rowling and/or her people.
Short of knowing how Harry Potter would input the Konami Code, we can at least rejoice that we know how he'd input big-head mode in NBA Jam. Engorgio Skullus!