Varanus rainerguentheri is a member of the indicus-group and therefore a member of the subgenera Euprepiosaurus. The dorsal is very dark black with scattered blue scales, forming spots and occelli, which are sometimes arranged in up to 9 bands across the back. The tip of the snout is bright blue, the lower jaw is white and along the throat is an area of bright turquoise which forms a very attractive V-shaped pattern on the neck. All 4 limbs are heavily speckled with turquoise spots which form occelli on the upper legs. There are 138-139 scale rows around mid body.
A row of blue scales extends from the lower part of the eye to the upper edge of the ear. The throat is light colored with numerous dark spots, forming a reticulated pattern on the sides.
Like other members of the prasinus-group the tail is strongly prehensile, with 22-23 symmetrical blue bands on a black back-ground coloration. It is approximately 1.95 times as long as SVL.
The nostrils are round and are situated almost evenly between the eye and the tip of the snout. V. macraei can grow up to 100 cm total length.

The preserved holotype of Varanus rainerguentheri was collected at Jailolo on the Moluccan Island of Halmahera, Indonesia. Another live specimen is in a privat collection, which originates from the same locality.

Till now nothing is published on captive husbandry of this species. Because it is relatively close related to the other members of the V. indicus-group, the enclosure type would be similar as for these monitor species.