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)
- Millie is one of six engines in the 2016 series not to have any variants.
- Millie is the only engine to have the same bag code in the 2016 and 2017 series.