I Am a Rock is a humanoid Stand of a height similar to Yotsuyu's.
Its shoulders and upper arms are limited to thin pipes. Long shoulder pads, fixed to its torso, bear short, evenly spaced spikes; along with its chest, head, a transparent dome covering its head, and the back of its hands.
Its head is smooth and featureless except for its spikes; eyes vaguely articulated by muscle or brow around it, and a small, thin-lipped mouth.
In conjunction with its very thin waist, its legs appear to be in the shape of hammer pants.
Selective Gravity: This Stand imbues a target with a powerful gravity that causes a single, specific type of object to gravitate towards them by any means necessary (shown first with flower pots, then chestnuts). These objects will seek to imbue themselves (either as a whole or in pieces) into the "core" of the target and can only be avoided by exiting the user's range.
Yotsuyu must be able to touch the person in some form in order to begin the chain reaction, after which any object of his choosing is drawn to the person. It seems that in order to consecutively utilize this ability, he must touch his target after every usage to change the type of object he wishes to attract.
Yotsuyu attacks Josuke by causing heavy flower pots to converge on him, nearly crushing him. Even when the pots are shattered, the fragments continue to dig into his skin. Only when Josuke uses Soft & Wet to steal the weight of the fragments does he free himself. It is also capable of drawing object towards itself at any given moment, although it is unknown if this ability extends beyond rocks as both times it was used Yotsuyu applies it to stones in his immediate vicinity.
The Stand also appears to have an effective distance, as when he uses it to send all of the Chinese chestnuts in their shells to attack them, once the two are in the basement and out of his line of sight, the chestnuts stop advancing.
Miscellaneous Powers (tentative): Yotsuyu first uses his Stand to restrain and assist in waterboarding Yasuho. After first producing a strange film from his eyes and mouth, he places it over Yasuho's face, and begins pouring water onto the film, which directs it all into her mouth/nose. When he is tripped by an origami banana bunch empowered by Paper Moon King and falls on broken glass, the film dissipates.
In terms of speed and power, this Stand is capable of overpowering an ordinary human like Yasuho Hirose but despite Yotsuyu's confidence in a frontal assault against Josuke, Soft & Wet was easily able to avoid I Am a Rock's punches and responded by delivering a single strike to its face which concluded the exchange. Considering Soft & Wet has high physical capabilities, it is difficult to determine how successful Yotsuyu would fair against other Stands in regards to physical combat.
An aspect of this Stand's ability is shown while Yotsuyu Yagiyama attacks Yasuho in Tsurugi's secret room in the abandoned fruit storehouse of the Higashikata estate; in a successful attempt to draw out Paisley Park.
Later, it is used in a sustained attack on Josuke, aiming to kill or prevent him from ever recovering his lost memories. Its powers are utilized first to attract flower pots to Josuke, and then Chestnuts and finally bottles of pesticide.