A unique Stardust Guardian minion will follow the wearer. It does not count against the player's minion capacity, and its function differs across versions:
On the Desktop version, Console version, Mobile version, and Nintendo Switch version, the Stardust Guardian is passive until an enemy is within a 30-tile radius from the player. It will quickly charge even through blocks towards the enemy, which it then strikes rapidly with a flurry of punches that each deal ~30 summon damage. Once there are no more hostile entities within range, the Stardust Guardian will return to following the player passively.
On the tModLoader version, it is passive until activated by double-tapping the ▼ Down key, which places it on the nearest block beneath the cursor position. Once placed, the Guardian becomes a sentry-style minion that can chase enemies for very short distances before returning to its original position. It periodically triggers explosions that deal 20 damage and cause enemies in the blast radius to target the Guardian instead of the player. It is deactivated by holding the ▼ Down key, which causes it to return to following the player passively.
Like all armors made from Luminite, equipping Stardust armor makes the player give off light, in this case white. Unlike other Luminite sets, equipping just one piece of the set gives off the full amount of light.
Light given out from the armor does not stack with Shine Potion, and the brightness is exactly the same as Shine Potion.
Using Stardust armor and accessories and buffs, it is possible to have 11 minions, not counting the Stardust Guardian.
While it is a potent offensive set, Stardust armor has relatively low defense, and although its ability to attack any enemies that come within a far distance of the player compensates somewhat, the Stardust Guardian does not protect the user against projectiles which leaves them vulnerable. The Valhalla Knight's Breastplate can be substituted into the set to provide much greater survivability, sacrificing the Guardian, and two minion slots. It may be worth it to wear the full Valhalla Knight armor instead of the Stardust armor, as it has much more defense, movement speed, health regeneration, and 3 extra sentries at the cost of 5 minions, the Guardian, and 6% minion damage.
The Stardust Guardian can move through blocks to attack enemies regardless of whether or not it has targeted the player. This can be exploited by walling oneself in, allowing the Guardian to take care of enemies (this method may be futile to some enemies, such as the Cursed Skull).
The Stardust Guardian is affected by whips, including summon tag damage and critical strike chance, and debuffs which take effect when the afflicted target is hit by a minion.
Stardust armor has the lowest defense of the four Luminite armors.
The Stardust Guardian was originally created as a reference to Algalon the Observer from the massively multiplayer online role-playing game World of Warcraft. However, due to the community's enthusiasm in comparing the Stardust armor to Star Platinum from the Japanese manga/anime Stardust Crusaders, which is the third story arc of the JoJo's Bizarre Adventure series, lead programmer Yoraiz0r has acknowledged the resemblance and said the armor can be a reference. The similarities have become more apparent with the rework of the Star Guardian's attack style in 184.108.40.206.: A barrage attack, referencing "Stand Barrage", an attack used by humanoid Stands (A "spirit" that helps it's owner fight), where the stand unleashes a flurry of punches.