From: Achromatic | #023
Harry faces things with immunities all the time, it wouldn't be anything new to him to see a spell not work.
Specifically, he's even faced an enemy immune to everything until he figured out his weakness (it was a fear-eater if you're curious). This included fire. In the end, Harry came out on top. He's extraordinarily bullheaded, and until he dies he'll keep on going and going.
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Sburbopolis, Homestuck RPG: http://www.gamefaqs.com/boards/8-gamefaqs-contests/60981373