Use this in long range maps, so you can have more space to strafe around the map.
Use homing missile weapons or gadgets and aim (in)directly at its users. That way, you will be able to take out its users easily, unless if they are able to escape the homing projectiles.
In cooperative modes, like Team Fight, if they did escape, have a teammate that can help you take out its user(s). If you are playing in Deathmatch fight at close range, which will harden their escape.
Do not stand still while sniping. Try strafing like its users, even without the Demolition Mask itself, and sniping at the same time. You could use an accessory or two to help you, like the Berserk Boots and the Burning Tiara.
Players equipped with this are quite common in close range maps, especially in Silent School, where most royal players play on. In corridors, these type of players do not have much space to strafe in, so you have the chance to use highly efficient Heavy weapons like the Ghost Lantern and the Big Buddy.
Simply stated, there is no proper way of countering users that use this as their helmet. Most of the wear is instead just for boosters, what you should really be focusing on countering is the weapons that your enemies are using.