Electro Saw is a stage hazard that first appeared in Kirby Star Allies. It is a rotating electrified buzz-saw which follows a set path along a metal guide wire. It cannot be inhaled or attacked with normal weapons, but Splash-based attacks and the Artist ability can destroy it. When destroyed, it drops Point Stars.
Electro Saws are capable of breaking through large metal blocks. They can also be found forming the second HAL Room in the game. Whether or not more saws will replace ones that are destroyed depends on whether the guide wire leads off the edge of the area or not.
Next, please look at the second image. This is a hidden room that's somewhere in the Fortress of Shadows, Jambastion. There are many Electro Saws (an electric obstacle that moves along rails) inside, and the rails are shaped like the three letters, H, A, and L.
— Yuki Endo, Level Design Director for Kirby Star Allies, from the Switch News Post 'Find hidden rooms with these two hints!', posted on April 12th, 2018