The E-75 (Heavy Tank) was a prototype heavy tank designed by Germany during World War II. It was part of the "Entwicklung" (EN: "development", or "evolution") series of tanks, intended to streamline tank production. The "75" means that it would have been in the 75-100 ton weight class. However, the E-75 never got off the drawing board. Had it actually been produced, though, it could have become the Tiger III.
In the later years of World War II, Germany had produced a wide variety of tanks and other armored fighting vehicles. While effective, they were complex to manufacture and were beset by a number of drawbacks. Thus, it was decided to produce a series of cheaper & simpler AFVs, which gave rise to the E-series tanks (not to be confused with the E-series robots). One such tank was the E-75. Though not intended to be an improvement in armor & firepower over existing designs, the E-75 would have made modest improvements in these areas had it been produced.
The E-75, being a real-world vehicle, had no "special powers" in the Sonic sense. However, plans for the vehicle indicated that it would probably be equipped with a 105mm or 128mm main gun. In real life, the JagdTiger tank destroyer was equipped with a 128mm gun, which proved to be very effective in destroying enemy tanks. Additionally, armor thickness of the E-75 would have ranged from 5 to 10 inches. Thus, we can get an idea of how effective the E-75 might have been. However, the JagdTiger was also plagued by mechanical problems & fuel shortages, and German factories couldn’t make enough of the 128mm guns to make a difference, so they sometimes had to use 88mm guns as substitutes. Given these conditions, it’s very likely the E-75 would have suffered as well.
The E-75 is a focal point of BearfootTruck’s fanfic "Two Kinds of Heroes", where a factory is being constructed near Stalag 13 for the production of these big bad battle machines. Owing to the nature of the machine, the factory is heavily reinforced and heavily defended against Allied attacks. However, a small team of specialists just might be able to destroy it, and that’s where our beloved blue hedgehog and his friends come in. Their timing couldn’t have been more perfect, as a few E-75s have already been completed and are almost ready for the battlefield. However, they blow up the factory and the tanks along with it.