Character Ideas is a fan-fiction thing to make.
Harmood is a purple Narrow Gauge engine. He is introduced in A Bad Day For Harmood. Many accidents he causes: scaring his coaches, bending the rails apart, derailing at some points and falling down on a canel.
Flick is a little Narrow Gauge engine introduced in the episode, "Skarloey & Flick". Flick causes trouble by crashing into the rocks. He is sent to the sheds in disgrace by Mr Percival.
Weasel is a gray Class 8 Shunter. He was introduced in the episode, "Pop Goes The Weasel". Weasel tried to sent Percy away by telling lies about him to the trucks. The Fat Controller find out about Weasel's lies and sent him packing.
Nikhil is a red tank engine who was introduced in the episode "Thomas and Nikhil". Nikhil doesn't listen to Thomas's advice of going slowly with a load of heavy machinary and has an accident by crashing into Edward's train of coal trucks. Thomas shunts Nikhil to the steamworks so Victor can fix him.
Philip is a yellow tank engine who was introduced in the episode "Don't Pump Your Pistons yet, Philip!" and wears some of Duncan's face masks. Thomas and Rosie tell Philip not to pump his pistons before leaving because it wastes coal and water, but Philip doesn't like Thomas interfering and pumps his pistons too much and end up running out of coal and water.
Kyfer is a red saddle tank engine who has the same basis as Bill and Ben who was introduced in "Kyfer Helps Out". Kyfer decides that he would help Henry with his jobs, but Henry wants to manage on his own which makes Kyfer sad. Then, he follows Henry by trying to be his back engine but makes Henry and the trucks come off the rails.
Stephanie is a big green tank engine who was introduced in "Thomas, Percy and Stephanie". Thomas and Percy are ordered by the Fat Controller to take Stephanie around Sodor. Stephanie smiles when she sees the sights, but Arthur tells Stephanie that she's a green catterpillar on wheels which makes Stephanie sad. But when Arthur derails, Stephanie brings Rocky to lift him back on the rails and Arthur then says sorry to her for calling her "catterpillar on wheels".