Reuniclus is a pale green Pokémon surrounded by a blob of translucent, green gelatinous substance. It has a large, round head with a thin stripe down the center. Its eyes are black and oval, while its mouth is red and triangular. Its body is small with stubby arms and legs. However, there are several round objects floating next to its arms. These objects increase in size and darken in color the further they are from the body and form arm-like appendages. The gel around these appendages forms three-fingered hands. Above its head, two rounded, triangular objects are suspended in the gel, giving the impression of horns or ears. The gel forms a stubby, round tail at the base of Reuniclus's body. Reuniclus controls its powerful arms using psychic powers. It can form a network with the brains of other Reuniclus by clasping hands with them.
Reuniclus and the rest of its evolutionary line seem to bear reference to cells, with the green substance surrounding their bodies resembling cytoplasm and the objects inside their bodies representing organelles. The line down its head also resembles a cleavage furrow in cell biology. It may also make allusion to the embryonary stages, specifically when the embryo is fully developed to become a fetus, while the green jelly may represent the amniotic fluid. The way its organelles are lined up in Reuniclus's arms resemble the generic meter for volume control, most likely referencing the ability to amplify its powers. Reuniclus also has a strong resemblance to a homunculus, due to its larger ears, mouth, and hands, to represent a homunculus's ability to amplify. It may also be based partially on an amoeba, with its arms resembling pseudopods.