Dominic Onion is a mage from Lunar Isle and hosts the Nightmare Zone minigame. As a member of the Moon Clan, he specialises in dreams.
As a young child, a plan came to him in a vivid dream where he saw himself running a successful business from a great structure. He told his father about it, who laughed and said he should be a banker like his ancestors. He refused and wanted to find out what that dream meant, so he studied to find out more about Magic, particularly oneiromancy and dream interpretation. Once he had learned enough, he left Lunar Isle attempting to find the location where he built the huge tower. Since he had not found it or gathered enough money for its construction, he decided to set up a small business north of Yanille selling dreams to people, which became known to the people as the Nightmare Zone.
- Dominic Onion is the solution to the medium anagram clue: I DOOM ICON IN. The answer to the challenge scroll How many reward points does a herb box cost? is 9500.
- Dominic Onion is the solution to the elite cryptic clue: 'See you in your dreams' said the vegetable man.
- Dominic Onion's name is a pun on the word "dominion," referencing the Dominion Tower in RuneScape 3, a tall tower where players can fight enemies they have previously encountered in quests, similar to the Nightmare Zone. The "huge tower" from Dominic's dream may also be a reference to the Dominion Tower.
- An alternative explanation for his first name may be as a reference to the character Dominick Cobb, the main character from the film Inception, which features a similar premise involving entering and fighting within dreams.