Merlin (a.k.a. Merlin the Invisible) was a Bio-Fused experimental tender engine.
Biography
Nothing is known about Merlin's past before he was Bio-Fused into a SR King Arthur class 783 Sir Gillemere tender engine.
One day, he was locked in jail with Toby and Kevin.
He was than assimilated by Project G-1 when Diesel crashed into its container.