Advantages

Rock is able to defeat scissors through the means of breaking them, or dulling them, even though rock is rock and scissors are metal.

Countering Rock

Rock is defeated by paper, because “paper covers rock”. This creates a Schrödinger’s cat effect, where we no longer know if the rock is alive or dead rendering its mere existence an enigma.

Speculation

It is possible that the rock is actually a representation of Dwayne The Rock Johnson in which case the game plays completely the same.