You Killed My Family: Prepare For Hell

After Sirius' death, Harry reflects upon his life and realizes that, ultimately, Snivellus is to blame. Further inspection further supports his theory. So, what's a severely pissed off teen to do? Get revenge by pretending to be completely nutters, of course! Contains Evil!Snape, Good-but-Oblivious!Dumbledore, Powerful!Crazy!Harry, magical blocks, animagi, and Marauding