Not much is known about Ernst, as he is simply one of the many newts Waffle has. What we can assume is that he's normally in the crowd of newts that Waffle usually has around, whether they're playing hide and seek or relaxing at the Newt Pond.
Physical Appearance
Ernst looks like the rest of the newts.
Background Information
His name was revealed in "Mecha-Kitties" when Waffle was demonstrating how a vacuum cleaner funtions.
Due to this, Ernst is the second newt to have his name revealed in the show.