The alien race that is fought is known as the "Irata", being the name of Williams competitor Atari spelled backwards. One of the other new enemies is also named after a competitor, "Yllabian Space Guppies"; Bally Midway was a major competitor with Williams in both the video game and pinball markets. Another new enemy is the "Dynamo," which breaks into several small "Space Hums"; this is in homage to the song Dinah-Moe Humm by Frank Zappa. Three new arrivals, "Phreds", "Big Reds", and "Munchies", vaguely resemble Pac-Man, a game released in the U.S. by Bally.