Shadow Devil is a robot from the Devil series in Mega Man X Collection. He resembles the New Yellow Devil and has a bright red eye.
Mega Man X must do whatever he did in the first Mega Man game by dodging the blobs, except, the outline of the Shadow Devil will damage Mega Man X if he touches his outline. When his eye appears, Mega Man X must shoot the eye on a random appearance and the eye will shoot X so he has to avoid the shots. Now the Shadow Devil will now resemble the sixth Wily Machine from Mega Man 6, so it'll charge in the room and will jump until the eye appears. The Shadow Devil then repeats again.
The Shadow Devil is considered one of the toughest bosses in the entire Mega Man franchise. The other is Rangda Bangda.
The Shadow Devil's stage is similar to Quick Man's stage in Mega Man 2.