20th Century Boy appears generally like a hollow piece of armor, composed of a headpiece, two large shoulder pads from which hang two long, branching straps, and a shell at its back from which grow two more comparatively plain straps. Blank-eyed, its head bears two long, vertical antennae; a bolt runs through it from shoulder to shoulder; and it is marked by a motif resembling a small hand of three simple fingers, both on its head and at every end of its branching straps.
20th Century Boy is purple and cyan in the colored manga.
20th Century Boy has no special offensive capabilities but its defence is exceptional. Although Magent Magent must be immobile to become invulnerable, there is no way to bypass its defence.
As a result, only sneak attacks and returning the immobility against Magent Magent are effective against him.
Whenever Magent Magent activates 20th Century Boy and kneels to the ground, he becomes impervious to all damage.
All energy and incoming projectiles are redirected away from Magent Magent into the earth or air, making him immune to any damage, be it from Stands attacks, Steel Balls, bullets or explosions. It even prevents Magent from other dangers like drowning. 20th Century Boy's ability has been explained as belts stretching out like earthing wires, and redirecting all the energy from enemy attacks into the ground.
The downside of this ability is how it is activated, requiring Magent Magent to expose himself or stay immobile. Thus, one can lure Magent into dropping his guard and know that he won't be able to react to sneak attacks fast enough, or take advantage of Magent's immobilization to tie him into a precarious situation and thus trap him.
- ↑ 
- ↑ 2.0 2.1 SBR Chapter 52
- ↑ 3.0 3.1 SBR Chapter 62
- ↑ JOJOVELLER: STANDS - Comments by Hirohiko Araki
- ↑ 5.0 5.1 SBR Chapter 53