Asteron, called Telstar (テルスター) in the Japanese manual, is a starfish-shaped Badnik from the 16-bit version of Sonic the Hedgehog 2 found in Metropolis Zone. Asteron is found in the walls and normally can't be destroyed. When you approach, they begin to flash, then explode, with spikes flying in five different directions.
The enemy reappears in Sonic Pocket Adventure's Gigantic Angel Zone, acting the same as in their earlier appearance.
Asterons also feature in Sonic the Hedgehog 4: Episode I's Mad Gear Zone. In this appearance, they now twirl around before they explode, making them easier to spot and avoid.
In Sonic Mania, Asterons can be found in Act 2 of Press Garden Zone, though they never appear as a regular enemy. During the level, shuriken launchers similar to the arrow-shooters from Sonic the Hedgehog 2's Aquatic Ruin Zone shoot out Asterons, which act identically to the aforementiond arrows and can be used as temporary platforms by the player. They are difficult to recognise in this appearance, as only the side of them is visible rather than the more familiar front view. They also appear in more recognisable form in the Zone's main boss fight, where they are used as shuriken by the Heavy Shinobi. At first, he throws only one Asteron, but once he has only one hit remaining he begins unleashing them in waves of three at a time. They can be destroyed when on the ground using a Spin Jump; if left unattended, they explode and release spikes just like their previous appearances.