On your missions you might run into
Exploding Walkers. These are former soldiers that carry explosives on their belts and are marked by a grenade icon.
Shooting these walkers causes a big
explosion damaging everyone (both walkers and survivors) within the radius, even through walls.
Explosions have a chance to ignite any surviving walkers in the range and make them burning walkers. Other exploding walkers in the radius explode in a chain reaction.
Notice that explosions also
cause threat so be careful whether you trigger an explosion in Overwatch or not.
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The Walking Dead: No Man’s Land GUIDE