The Hellions are a street gang in the world of the City of Heroes MMO that uses magic and fire for power.
According to the late Jimmy Hellfighter, the Hellions have a cult-like obsession with fire and blood, believing it to be a gateway to mystical power. Often they will sell their services to unscrupulous groups for money, although it is merely a means to an end for them.
"Derf" is a low-level member of the Hellions who is often the idiot that ends up getting caught or beaten up.
(Please see their Paragon Wiki entry for more information.)
Hellions were seen in numerous comics set in the "City of Heroes" world.