Millie (also known as Classic Millie) is an engine in the Classics theme.
- Robot Millie
- Millie as Harley Quinn
- Warrior Millie (from 50 MINIS!)
- Millie as Catwoman (from DC Super Friends 9-Pack 1 (2016) and DC Super Friends 4-Pack 1 (2016))
- Millie as Sandy Cheeks (from SpongeBob SquarePants 9-Pack)
- Construction Millie
- Night Time Millie
- Peacock Millie
- Millie as Bumblebee (from DC Super Friends 9-Pack 2 (2017))
- Watermelon Millie
- Neon Glow Millie (from Neon Glow in the Dark Pack 2)
- Parrot Millie
- Millie is one of six engines in the 2016 series not to have any variants.
- Millie is shown on the Australian 2018 second series checklist, but is not in the 2018 series.
- Millie is one of the fourteen engines in the 2018 series not to receive a Classics variant.
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