Predator Mode is used in areas with several armed enemies, who can easily overcome even the most experienced players if they were taken head-on. Thus, instead of using Freeflow Combat, players are supposed to target enemies with stealthy hit-and-run tactics to pick them off without being overwhelmed by their superior firepower. Ideally, players are to target isolated thugs and take them out one at a time by using Takedowns or gadget traps while they remain undetected.
In most Predator Rooms, Batman can grapple up to a Vantage Point to see the area from above. This allows Batman to see most of the enemies from a single location and then glide behind unaware enemies, taking them out with a Silent Takedown. However, if Batman's enemies realize he is using these vantage points, they often either mine them or shoot them down to prevent their continued use. In Batman: Arkham Knight, Batman can instantly travel from Vantage Points to underground vents (and vice versa) via chutes near the ceiling.
Batman can also use vents to his advantage, hiding under his enemies. This allows him to move silently, but only in areas where it was possible. Batman can perform a Takedown if he was right under his enemy. Before Arkham Knight, vents are mostly simply small areas that the player could hide in, but in Arkham Knight, they became a major way of moving around, and often covered most of the bottom floor, with a few usable exits. If enemies see Batman in/entering the vent, they would fill the vents with burning gas, which destroyed the vent cover and damaged the crimefighter in the process, unless he was able to escape beforehand.
In Batman: Arkham Asylum, Batman: Arkham City, and Batman: Arkham Origins, most enemies carry an alarm which went go off if they are knocked out. As the alarm activated, the announcer noticed it, and informed the remaining henchmen. However, that took a few seconds, and allowed Batman to escape the area. In Arkham Knight, enemies no longer carried those alarms, but their leaders regularly asked for updates (After 3 Silent Takedowns). and became suspicious if somebody didn't answer.
In both Batman: Arkham City and Batman: Arkham Origins, some Predator Rooms have a special, non-hostile NPC in them. After the enemies become aware of Batman, there's a chance that they will walk to the hostage and take him/her as a human shield. If this happened, the player is forbidden from using some gadgets against that particular thug, and needed to sneak behind him, when his back was turned. If that thug saw Batman, he shot the hostage, and the player failed the challenge.