Batman has always recognized the need to be prepared in case one of his Justice League allies turned against the team, and at times, this habit of keeping contingency plans has itself been a source of conflict between the Caped Crusader and his superpowered friends. However, the history of the Justice League has proven that not only is Batman right, but that perhaps he hasn't been prepared enough.

Batman's contingency plans acknowledge that there is a thin line between heroics and villainy, one that can be crossed unwittingly, or for the seemingly "right" reasons. Despite what the other heroes might think, any one of them could pose a grave existential threat to the world, and Batman knows this. Below are ten corrupted versions of heroes that prove Batman needs more anti-Justice League plans.

10 Hecate Wonder Woman

First seen in Justice League Dark: The Witching Hour #1 – by James Tynion IV, Jesus Merino, and Romulo Fajardo Jr – this story reveals that Wonder Woman was marked long, long ago as a child by the Witch Goddess Hecate. Diana was one of five women marked, and when the time came, Hecate took control of their bodies, granting them unbelievable magical power, while also turning them into puppets for her to manipulate. This evil version of Wonder Woman was such a threat that in order to escape Hecate's control, Wonder Woman was forced to side with a far more dangerous villain.

9 Future Flash

The Flash is one of the greatest heroes alive, one who has a surprisingly good relationship with most of his enemies. It's not unusual for Flash and his Rogues to work together if the situation calls for it. However, one future version of the Flash made it his goal to not only kill all of his enemies, but also himself at the end of it. Future Flash discovered a rupture in the Speed Force, as seen in Flash #30 (2014) – by Van Jensen and Robert Venditti – that causes him to slow down over time. As a result, he was unable to save the lives of many people in his career, including Wally West. By traveling back in time and killing present Flash, Future Flash hopesd to absorb enough energy to seal the rupture and restore his powers.

8 Sovereign's Aquaman

Hailing from a dark alternate future where he serves a corrupted version of Hippolyta, this Aquaman arrives in the present and absolutely decimates the Justice League. This dark version of Aquaman has powers surpassing the Justice League and is able to take them on all at once, using a mix of brute force and plans designed to target specific members of the League that would make even Batman jealous. The most alarming thing about this was the fact the attack was entirely unprovoked, with the Justice League being taken completely by surprise, showing that Batman's advanced preperations for these kinds of scenarios is essential.

7 Upside Down Man Zatanna

Magic is a major focus in the DC Universe, but not all magic is good magic. This is best illustrated by the villain the Upside-Down Man, a horrifying eldritch monster. The Upside-Down Man was a part of the Otherkind race, beings that represent the horrifying and dark possibilities of magic. It was the Upside-Down Man's goal to devour all magic and life in the DC Universe, and it took the entire Justice League Dark to contain him. They weren't even able to stop him fully; instead, they trapped him within the body of Zatanna. As a result, every time Zatanna used magic, the Upside-Down Man would get one step closer to taking over her body and breaking free.

6 Parallax Hal Jordan

After the destruction of Coast City, Hal Jordan was driven to madness by grief. Every single person he knew, including his father, had been killed. He tried using his Green Lantern ring to recreate the city, but this was a violation of the Green Lantern Code, and his fellow Laterns tried to stop him. The result: Hal Jordan killed every Green Lantern he came across, before absorbing the energy of the Central Battery on Oa, becoming the ultimate villain Parallax. Hal would then go on to try and reset time in the Zero Hour crisis event. This was later retconned to Hal being controlled by the monster Parallax, but originally, his actions were his own.

5 Grid

When Victor Stone gained his cybernetic body, he realized the potential of his power included being able to spy on every superhuman on Earth at once. While Victor felt this was potentially necessary, he wasn't willing to consciously commit invasion of privacy on that scale. Instead, he left it up to a subconscious subroutine he referred to as "the Grid." Unfortunately, as Grid continued to monitor people it began to learn and grow, eventually becoming fully sentient, a mind independent of Victor's. When the Crime Syndicate invaded Earth, Grid saw its chance and took control of Victor's cybernetic components, building a brand-new body for himself, using it to join the Crime Syndicate in taking over the world.

4 The Crime Syndicate

Batman's contingency plans may have proved necessary, but they have nevertheless caused tension between him and the team. The problem here is the assumption that Batman's plans are actually for them. There is an entire multiverse to deal with, and Batman is aware that even if his allies never go bad, some alternate timeline version of them surely has. For example, the Crime Syndicate, an evil Justice League, have invaded DC's main Earth several times. While some of them have different weaknesses, such as Ultraman, most of them function the same as their counterparts in the main DC continuity. Batman knows his teammates better than anyone, and can use that knowledge to defeat their villanous counterparts.

3 Eclipso's Justice League Dark

Eclipso is one of the most terrifying villains in the entire DC Universe. He is the first avatar of God's wrath, a divine being who can essentially do whatever he wants. His main power is the ability to draw out the evil desires in a person's heart, turning them into the absolute worst versions of themselves. Eclipso has already taken over both the Justice League and Justice League Dark on different occasions. Eclipso is only defeated by direct sunlight, which is a problem when his presence causes an eclipse, and he can control the likes of Superman with ease. As with any villain that can exert control over the will of heroes, having a way to contain the heroes until the villain is defeated is absolutely neccessary.

2 Jokerized Justice League

In Scott Snyder and Greg Capullo's Batman: Endgame, the Joker hit the Justice League with personalized doses of Joker Toxin, unleashing their worst impulses and rage. This story was notable for showcasing Batman's Justice Buster suit, a giant mech suit built specifically to deal with the other members of the Justice League in open combat. Many of the League members critical of Batman's contingency plans argue that his plans could be stolen and repurposed by their enemies, and while some of his plans may be difficult for someone other than Batman to implement, the Justice Buster suit could be devastating if it were to fall into the wrong hands. Or, it could be the key to saving the world from a future Just League gone bad.

1 The Batman Who Laughs

Even Batman himself is not immune to the possibility of turning, or being turned evil. Even Batman needs a contingency plan. The Batman Who Laughs was a twisted version of Bruce Wayne that was infected with a powerful strain of Joker Toxin, which eventually rewrote Bruce's brain, turning him into a twisted version of the Joker himself. With the construction of Failsafe, Batman has contingencies against even his own dark opposites across the multiverse, or a future version of himself that crosses the line somehow. This shows that Batman isn't just preparing for the need to take on the Justice League, he has contingency plans for himself as well.