Snap-Flash

The Snap-Flash is a small explosive gadget used by Robin. It is a small, slightly lethal mine that could be stealthily planted on an unsuspecting thug's back, and detonated to knock down the enemy and those close to them.

Harley Quinn's Revenge Incident
Robin used his Snap-Flash mine to explosively take out unaware henchmen while he sneaked into the Steel Mill to save Batman from a depressed Harley Quinn after the Joker's death.

Arkham Knight Incident
They could be used whenever you played as Robin. In combat, they work the same as before, and can be planted on downed enemies. However, in Predator Mode they cannot be planted on downed enemies, but instantly take out their target and sometimes those close to them, likely to compensate for the increased amount of enemies.

Gameplay

 * In the Harley Quinn's Revenge story, Robin can attach a Snap-Flash onto an object.
 * The Snap-Flash is unique to Robin. It can knock down nearby enemies to the ground for quite some time, opening Ground Takedown windows. Deathstroke's Neural Gas is used the same way (by attaching to a nearby enemy), but it functions like Batman's Concussion Detonator in that it merely makes enemies disoriented into staggering and punching air.
 * To use the Snap-Flash, Robin (and similarly, Deathstroke when using Neural Gas) has to be in very close proximity to an enemy, otherwise he won't deploy it. To get close enough, you can try doing a Beatdown, or using the Snap-Flash on an attacking henchman rather than countering him; in predator situation, simply sneaking up behind an enemy is enough. The deployment is slow and it leaves Robin vulnerable to attacks, which makes it even more difficult to use the Snap-Flash. Additionally, the Snap-Flash should not be detonated immediately after it's attached to a henchman in combat, otherwise the combo will break, therefore it's advisable to do at least an Evade first. Once deployed, the Snap-Flash can be detonated any time, even if the henchman it's attached with is taken out, and he will glow red in Robin's Detective Vision. Due to its difficult use for combat, the Snap-Flash is very rewarding: if detonated, it knocks down enemies nearby and grounds them for quite some time and it adds combo multipliers equal to the number of affected enemies, then points equal to that number x the current combo multipliers x 25, unlike any other attacks which only add 1 multiplier even if they affect multiple enemies at the same time. As such, it helps boost the combo and reach Special Combo multipliers very quickly.