Ruby Star

From the Super Mario Wiki

The Ruby Star is the fourth Crystal Star in the game Paper Mario: The Thousand-Year Door. The Ruby Star was originally owned by Doopliss, until Mario defeated the Duplighost in combat.

Mario receives the Ruby Star after Vivian joins his team to help him get his name, appearance, and teammates back. Together, they confront Doopliss (who is disguised as Mario). Ultimately, Vivian and the real Mario defeat the doppleganger and recover the Ruby Star.

This Crystal Star teaches Mario the move "Art Attack", which costs 4 SP. To use this move, the Player must draw circles around enemies with the Ruby Star. Encircling an enemy completely causes maximum damage, while cutting corners cuts the damage as well. If the player fully draws a circle around an enemy, it will cause 3 HP damage. If most of it, then 2 HP damage. If only partially, then 1 HP of damage.