In Scenario A, you face William again at the room where you call 
the large elevator. If Claire found it, use the submachine gun 
and he's as easy as pie, when he transforms, whip out that grenade 
launcher and put some grenade rounds right into that big mouth of 
his, for Leon, use that flamethrower, or if you decided to take it, 
the submachine gun for the first round, when he transforms, finish
 off the flameshrower on him and use that Custom Magnum if you got 
it, otherwise the regular magnum or upgraded shotgun work well, 
but he bounces around a lot, so make sure you bring plenty of 
health items, and when he goes into his transformed stage, he can 
hop up on the tops of those tanks, when he does, run around, so he 
doesn't smack you when he jumps off.