One Piece Episode 371 -

In , the "useful feature" refers to Gecko Moria's ability called Shadow Revolution . Shadow Revolution: Moria’s Manipulative Power

During the battle against the Straw Hat Pirates, Moria demonstrates that by manipulating a person's shadow, he can force their physical body to change its shape as well. One Piece Episode 371

Gecko Moria & Oars vs. the Straw Hat Pirates. Plot Highlights: In , the "useful feature" refers to Gecko