The following code requires the latest version of 
Diablo: Hellfire. It will not work on the original
version.
To access some secret Easter eggs in Hellfire, create 
a text file called command.txt and place it in your 
Hellfire directory. Next, place the following line 
in command.txt:

multitest;cowquest;theoquest;bardtest 

You can get a new character,The Bard.

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in the command.txt add: barbariantest it will add another 
new class, the barbarian. he reuses warrior artwork 
and has max strength of 270
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This enables LAN and modem games, two new quests 
(Cow Quest and Theo Quest), and two new character classes:

The Bard reuses the Rogue's art, but can wield two weapons 
at once and has the Identify spell as her natural ability. 

Transfer Characters from Diablo 
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To transfer your characters from Diablo to Hellfire, find 
your save file and change the extension to .HSV. For example, 
if your file is called RASSILON.SV then rename it to RASSILON.HSV.