Spotted paddle-tail newt
"Pachytriton" species are stout-bodied, smooth-skinned aquatic newts. Their heads are large and flattened, and they have conspicuous labial folds and short, stubby legs and toes. They breathe through both lungs and skin. 
"P. brevipes" ranges from 5.5 to 7.5 in as an adult. It has prominent labial folds, long digits, and smooth skin, which differs from the tuberculate skin typical of newts.
Ned's Newt
That night, Newton crawls from his bowl and gulps down several mouthfuls of Zippo. Thus, the "too much" warning comes true: Newton grows 6 feet tall, can talk (voiced by Harland Williams), and has the power to shapeshift. After Ned realizes this, he and Newton become the best of friends, but unfortunately, the effects of Zippo do not last forever. In fact, Newton often gets Ned into trouble, at which point the Zippo wears off and Newton shifts back to his smaller form, leaving Ned alone to bear the wrath of his elders.