The Explosive Batarang was a gadget that was exclusive to Batman: Arkham Origins Multiplayer that took out enemies in its blast radius. It used the exact same icon as the Sonic Batarang, but Batman could not use the Sonic Batarang in Multiplayer. Batman was the only one who threw it, as Robin never obtained that gadget. It could be leveled up by experience.
Batman Arkham Knight
The gadget returned for Batman: Arkham Knight, and was used during several Special Takedowns such as the Multi-Ground Takedown and Special Combo Batarang. The gadget wasn't capable of being used normally and was only used during special moves.
The Explosive Batarang exploded a few seconds after it hit a surface. It could be used to make enemies scatter, or to take out ignorant enemies.