Terraspin first appears in "The Legacy Artifact" when attempting to stop British robbers Percy Lancaster, Simon Williams and Rick Thomas from stealing the Everstone from Bellwood National Museum. The gangsters manage to trick him into allowing them to escape.
Terraspin goes out on the road and blocks off a line of cars - he didn't know that the gangsters' vehicle already escaped behind him on the other side. Angry drivers call in the cops, but Captain Rozum arrives, lets it go, and asks Ben to help him on the case instead.
Ben's body is lined with glowing green veins.
His skin moistens and greens before toughening up and cracking to provide his "scales" - his fingers join in that process and his flesh stretches and thickens before shaping itself into a turtle flipper. His legs do the same but turn into stubs. His melanin scrambles and creates splotches of turtle-like patterns.
Ben's back splits open and veins crawl out, forming a shell which automatically discolors and cracks to turn itself into a turtle's shell. His shoulders extend bone connections that internally lock with the shell's center and allow for rotation.
Ben's rib cage gives way at certain spots as muscle matter and bone marrow creates a cover over his chest and ages into a turtle texture. Ben's blood veins all are about to intersect before they cut off and blow air that fills his lungs and chest - the central point of all the air jets glows green and the Ultimatrix symbol forms.
The transformation is roughly four seconds.
Terraspin's appearance in Heroes of Evolution is one of the creature designs that undergoes several aesthetic enhancements, similar to Swampfire and his dead-plant ecosystem all over. Terraspin's skin texture and bodily detail/coloring all change to give a more turtle appearance, with much of his brighter coloring either darkening or fading.
Terraspin's shell has much intricate patterning to resemble the shell of an Eastern Box Turtle. It's cracked, and has a color combination of a many shades of green, yellow, black and brown, plus a bit of orange.
Terraspin's skin is changed from a bright green to a more dead-plant gray, with a strong mix of yellow and slime green plus detailed patterns to resemble a turtle's skin. It's far darker but is mixed in with signs of lighter yellows and brown in the cracks. This image is perhaps the best reference. Terraspin's skin isn't all that jagged, but contains a lot of cracks and scales and appears very rough and scratched to signify aging.
Terraspin's face is a mix of his cartoonish dinosaur-like face in the show and a real turtle's face. His facial skin remains light, and while not being encrusted in scales, it's still quite rough and the borders of his eyes and mouth are slightly cracked. His eyes have splotches of yellow and orange and while the shape is only slightly more rounded and relatively unchanged, his eyes heavily resemble those of an actual turtle.
Terraspin's abdomen mostly resembles an actual turtle's stomach - cracked with lines, yellow, and slightly scaled and faded. The holes for wind jets look more like they were smashed open though they all mostly follow the same shape - the inside walls when seen from the side look very rough.