The moment that Eternals was announced, imagery of the Celestials has been published through various concept art. In particular, one Celestial has been mentioned a few times by name in leaked merchandise, Arishem. This Celestial is allowed to judge whether a planet lives or dies and was also responsible for culling the Deviants on Earth thousands of years ago, although it caused nearly the death of the entire human race.
More merchandise has leaked showing more Deviants besides Kro, along with a design for Arishem. It even shows fans the spaceship that The Eternals will likely use as their home base in the movie.
Several Lego sets for Eternals have leaked, showing them fighting various Deviants. The first set shows the Celestial Arishem in a Lego set titled “In Arishem's Shadow,” which is advertised as being 30cm tall. There is a description included too, but there is too much glare to properly read anything significant, except that “Sersi transforms” something.
The second set, titled “Deviant Ambush,” shows Thena and Gilgamesh fighting an animalistic blue Deviant together. Thena has her glowing energy projected weapon, while Gilgamesh seems to be projecting energy on his fists to make his hits harder.
Next is “Eternals' Aerial Assault,” which shows Sprite and Ikaris fighting a blue flying Deviant, even showing both of them using their unique powers. This includes Sprite creating illusions and Ikaris flying and shooting cosmic energy from his eyes.
The final set gives fans a likely location for the movie and is called “Rise of the Domo,” which is apparently The Eternals' spaceship. This set includes Makkari, Ikaris, Thena, Sersi, Druig, and Phastos. The set will also include a cockpit, weapons room, and lab. One blurb also says that “when the leader of the Deviants arrives with his accomplice, it's time to take the spaceship into battle!”
WHAT THIS MEANS
Obviously, fans have learned since Iron Man 3 not to fully put their trust in Lego sets, but there haven't been any inaccuracies like The Mandarin's armored car for years. So, these Lego sets can at least be taken at face value, which shows more designs for the Deviants, which seem large, alien, and animalistic in nature. Some of them are small and able to fly, some are bipedal, while others are quadrupedal.
Something of interest in the “Rise of the Domo" set is that it says that the leadership of the Deviants arrives with “his accomplice,” singular, meaning that it seems likely that the bipedal one is meant to be Kro. However, his Lego figure is blue, while his Legends figure looked more green. It could be that they were both based on different designs for the character or that Kro will have multiple forms in Eternals, as he can shapeshift in the comics too.