It is possible that Sharpshot is based on Toothless in the books as he matches Toothless' description in color, size, behavior and overall design.
Sharpshot is also the only trained Terrible Terror that is shown to have more than one skill.
Sharpshot has the typical appearance of a Terrible Terror and is about the size of a small dog. It's main body color is dark green with reddish-brown highlights.
Sharpshot has a mellow behavior; when first chosen by Hiccup, it simply chattered to itself and twitched its head around. In a way, it behaves much like that of a trained hunting falcon, perching on Hiccup's arm after completing a task.
Sniper Fire: Taking advantage of the Terrible Terror's ability to launch its fire breath with pinpoint accuracy, Hiccup trained his Terrible Terror to fire on command and in rapid bursts. This allows Sharpshot to take out multiple targets with efficiency.
Hand Signals: Sharpshot is able to understand basic commands through hand signals.
Human Speech: Sharpshot also seems to understand some human speech as he looks at Hiccup when Hiccup says his name.