Agents Turned Odd
- Odd Todd - Let oddness happen, created odd-causing gadgets, and released a Pienado. This all led up to him not being allowed to be part of Odd Squad.
- Olga - Stole half of everything.
- President Obbs - Tried to take over the world by mind-controlling Odd Squad scientists.
- Weird Tom - Stole Odd Squad papers including gadget plans. He then forced Odd Squad to shut down in an act of revenge for not being allowed to become a full-fledged agent.
- O'Duffey - Worked for Party Pam for a little time.
Undercover Agents, Betrayed the Villains
- Evil Mime - O'Donahue, to figure out what the Evil Mimes were doing and to stop them.
- Patternista - Ms. O testing Oprah if she could take her place.
- Kooky Clown - Olive, to win back Odd Squad tube map.