Episode XV: Special Engines was uploaded on October 5, 2014, and is the fifth episode of the second season.
- Bill and Ben
- Sir Topham Hatt
- Mavis (does not speak)
- BoCo (does not speak)
- James (cameo)
- Donald and Douglas (cameo)
- Henry (cameo)
- Oliver (cameo)
- Thomas (cameo)
- Diesel 10 (cameo)
- Annie and Clarabel (cameo)
- Sidney (mentioned)
- James Riddle: Toby
- DarthWill3: Bill and Ben and Diesel
- EnterprisingEngine93: Edward
- RightonTracks10: Percy
- Thomas1Edward2Henry3: Everyone else
- This is the first episode to feature DarthWill3 as Bill and Ben and would be his only time voicing The Twins until The 2018 special Revenge of the Ghost Train.
- This episode was also the return of RightonTracks10, but as Percy instead of Thomas. To add to that, it is the first episode since Stuck! to feature James Riddle.
- The episode was originally planned for Mid-August release, but it was then pushed back to September so T1E2H3 could work on his own, non-Thomas films. Then, school started with more than expected amount of work, so the episode was further delayed.
- This marks the first proper appearance of Hilltrack's Trainz Routes's Bill and Ben models.
- The policemans "Oi! You!" from Thomas in Trouble/Thomas Breaks the Rules can be heard at the beginning as a joke.
- Henrietta is given a face for the first time. The face (which is really Rusty's) matches her face from the RWS rather the TV Series. It can also disappear and reappear.