Uni Uni belongs to the Sea Urchin-like Orbinaut series. As such, they look similar to their other variations. They have a green spherical body with wide eyes and four yellow spiked balls orbiting their body. They usually have black eyes, but had cyan eyes in Sonic Colors and Sonic Lost World.
In Sonic the Hedgehog 4: Episode I, the Uni Unis' design is more detailed. They have two lines encircling it vertically and one horizontally. They also have two black bases on both sides of their body.
Sonic the Hedgehog (16-bit)
The first appearance of this Badnik was in the original 16-bit version of Sonic the Hedgehog, where it served as an enemy. This time around, this Badnik is referred to as Uni Uni (ウニウニ,Uniuni?) in Japanese material, but is unnamed in western materials. In this game, the Uni Unis are found around the highways of Star Light Zone.
In gameplay, the Uni Unis are a bit more cool-headed than the Unidasus, namely by keeping their spiked orbs orbiting their bodies. While this means that the player does not have a tricky attack to avoid, they are virtually impossible to hit. However, the player can slip under them with a Spin Attack. They are best defeated while the player is invincible, although the player can also destroy them with a well-aimed hit or with a direct attack immediately after gaining invulnerability from taking damage. Also, due to their constantly orbiting spiked balls, they are hard to avoid at high speed. In case they are defeated though, they release an Animal.
Sonic the Hedgehog (8-bit)
In Sonic the Hedgehog (8-bit), the Uni Unis appear as enemies, but only in Sky Base Zone Act 1. Their appearance is also different, having an orange body surrounded by yellow spiked balls. Otherwise, they behave identically to their 16-bit counterparts. Like all the other Badniks, they do not have Animals as power sources.
In Sonic Rivals, the Uni Uni made an appearance as one of the game's collectible cards. It is again referred to as "Orbinaut."
In the Nintendo DS version of Sonic Colors, the Uni Unis appear in Planet Wisp, Aquarium Park and Asteroid Coaster. They look similar to how they did in Sonic the Hedgehog 4: Episode I, and appear both above ground and in underwater sections. Some Uni Unis block openings for the player to pass through while others move up and down. The best way to destroy them is by using Color Powers.
In the 2.5D side scrolling sections in the Wii U/PC version, Uni Unis usually hover back and forth in one place while their spiked balls orbit them laterally. These Badniks usually come together in stacks to create huge enemy walls. Exclusively in the Wii U/PC version, they drop their spiked balls in a rain when the player approaches them. However, this leaves them defenseless against attacks.
During the main 3D sections in the Wii U/PC version and throughout the Nintendo 3DS version, Uni Unis' spiked balls orbit them horizontally, but they do not drop them under any circumstances. They will also move towards Sonic when he gets close to them. In the Nintendo 3DS version, Uni Unis usually appear individually or in groups with different Badniks, but they do not drop their spiked balls like in the Wii U/PC version. The player is best advised to attack the Uni Unis from above without touching their spiked balls.
Powers and abilities
As an Orbinaut, Uni Unis have spiked balls that orbit their body at slow speed, unlike the Unidasu' which releases all their spiked balls at victims; it can thus be considered more of a defensive model rather than offensive one. This makes Uni Unis hard to defeat and dodge. They simply keep hovering forward, never stopping in place. Their spiked balls usually orbit them laterally, but in Sonic Lost World, they are occasionally seen orbiting them horizontally.
In the Sonic the Comic series published by Fleetway Editions, the Uni Unis' name is never mentioned and are instead referred to as Orbinauts. In this media, they are a part of Dr. Robotnik's Badnik army and are among the first generation of Badniks the doctor produced. Depending on the artist, the Orbinauts' design or coloration would be slightly different between each issue.
In the Sonic the Hedgehog comic series and its spin-offs published by Archie Comics, the Uni Unis' name is never mentioned and are instead referred to as Orbinauts. They were among the first generation of badniks produced by Dr. Robotnik. Over time though, the Orbinauts were rendered obsolete by more advanced robots and got decommissioned.
Following the events of Worlds Collide, the Orbinauts' history became nearly identical to that of their game counterparts.
↑ 1.01.1Pattenden, Mike (4 January 1993). "Robotnik's Badniks". Stay Sonic. Fantail. p. 36. ISBN 978-0140903904. "Orbinauts are extraordinary creatures. Part animal, part machine, all nasty, they can be found underwater in the Labyrinth Zone, on dry land in the Star Light Zone and in the Hilltop Zone in Sonic II. They come in all colours, some of them throw four spiky missiles, some have missiles but don't throw them, and some don't even have missiles (Sonic's careful of those ones because they can't be killed) but they all have a middle bit with big eyes, and they are all slow-moving. If Sonic sees an Orbinaut, back away from it. Jump over the missiles, then attack. If they don't throw their missiles, Sonic jumps over them."