Dangos are based on the armadillidiidae family of insects, more commonly known as pill bugs. They got protecting armor on their back, white eyes and small mechanical legs. Dangos come in two color schemes in each of the two Rounds they appear in. Green variations appear in Stardust Speedway, whereas orange-brown ones appear in Metallic Madness.
Sonic the Hedgehog CD
The Dangos appear Stardust Speedway and Metallic Madness. They are normally crawling slowly along the ground, but when they see Sonic, they curl into a ball and roll towards him, similar to the Spin Attack. While curled up, the Dangos are invincible, and attacking the rolling Dangos head-on with the Spin Attack will only inflict damage on the player. Dangos can be defeated with a Spin Jump while they are in crawling position though.
The brown Dangos in Metallic Madness appear aged and broken down in the Round's Bad Future and they roll much slower. However, the green Dangos in Stardust Speedway have not aged in that Round's Bad Future. Like every Badnik in the game, they are powered by Little Planet flower seeds which will pop out of them when they are defeated.
In Sonic Mania, the Dangos appear as enemies in Stardust Speedway Zone. Their attack pattern is consistent to ones featured in present timeline of Sonic the Hedgehog CD. As Act 1 takes place in Past timeline, Dangos have purple color scheme, which changes then to regular green in Present time of Act 2. Dangos are also now powered by Animals.
"Dango" is short for "Dangomushi" (ダンゴムシ), the Japanese word for "Pill Bug".
The Dango appears to use the same concept as the Roller from Spring Yard Zone. The only real difference is that they are invincible when in its ball form, while the Roller is easily destroyed.
↑While not listed in any instruction manuals, the in-game source code in 1996 PC release of Sonic the Hedgehog CD refers to this Badnik as "dango".
↑The PC version of Sonic Mania listed the enemy as "Dango" according to the internal files of the game.