Level skip:
Press 2 + 4 + E during game play. 

Unlimited lives:
Reset the game immediately after the phrase "Hewson presents... NETHERWORLD..." appears. Then execute the following BASIC commands to restart the program. 

POKE 12121,44
SYS 52320 
Unlimited lives (alternate):
Load or reset the game, then execute the following BASIC command before running or restarting the program. 

POKE 12116,44 
Unlimited time:
Reset the game immediately after the phrase "Hewson presents... NETHERWORLD..." appears. Then execute the following BASIC commands to restart the program. 

POKE 7698,44
SYS 52320 
Unlimited time (alternate):
Load or reset the game, then execute the following BASIC command before running or restarting the program. 

POKE 7698,18 
Unlimited energy:
Reset the game immediately after the phrase "Hewson presents... NETHERWORLD..." appears. Then execute the following BASIC commands to restart the program. 

POKE 8138,0
SYS 52320