Donald and Douglas are twin Scottish engines.
- Season 1 - Gordon Proves his Point (Douglas only), Crossed Lines (Donald only; Douglas does not speak), High-Speed Gordon (Donald only; Douglas cameo), Old Stuck Up (Douglas does not speak; Donald cameo), and Fire Engine (Donald only)
- Season 2 - The Missing Coach (Douglas only; Donald does not speak), Scrambled Eggs (mentioned in deleted scene), and Gordon Goes Foreign (Douglas only; cameo)
- Season 3 - Breakvan, Domeless Engines (cameo), Hullo Twins, and The Runaway (mentioned)
- Season 4 - The Deputation, Light Work (Donald only; Douglas cameo), Diesel's Big Idea (Donald only; Douglas does not speak), and Winter Mischeif (Donald only; Douglas does not speak)
- Season 5 - Rusty to the Rescue (Douglas only), Henry Sees Red (Donald does not speak; Douglas cameo), Out of Puff, Escape (Douglas only), Little Western , and Stepney's Special (Douglas only)
- Season 6 - Bright Spark (mentioned), Ballast, Resource and Sagacity, Donald's Duck (Donald only; Douglas does not speak)
- Season 7 - Mountain Engine and Percy's Porridge (do not speak)
- Season 8 - Edward's Exploit, Determination, and Toad Stands By (Douglas only)
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