Dude if u want to kill the last boss then get a house of the dead
expert and press normal mode on options.Then beat it.Now u hav unlimited credits.
(at least u can kill the last boss)

go on options switch the difficulty to very easy and set credits to 9 and lives to 5. even
then its really hard. i just barely beat him with 0 creds and 1 live torch thing.

if you want to beat him go to options and set it to very easy 9 credits and 5 fires