Screenslaver is the (former) main antagonist of Incredibles 2. The character was first revealed in a LEGO set for the Incredibles 2. The LEGO set in question is a LEGO set which includes Mrs. Incredible (or Elastigirl, however, she is wearing her Incredibles suit in the LEGO set), and Screenslaver. Although, this LEGO set is misleading, as the face behind Screenslaver's mask belongs to Winston Deavor. Edit
Screenslaver's mask seems to resemble a chlorine mask, as it has big round eyes, and a mouth that's pattern is similar to an air vent.
His costume seems to be all black, with a black scarf, black boots, black gloves, and a black belt.