History
The Jackals are former criminals and former champions of a top secret martial arts championship. They were handpicked by the mysterious Yotsuyama Group to work as body collectors from within the Tower of Barbs. As part of their jobs as body collectors, they are required to collect dead fighters as well as any equipment to sell among the black market. The Jackals are armed with equipment far superior to anything that can be found within the tower making them one of the deadliest enemies within the game.
In-Game
The Jackals spawn once a player takes too long on a floor after completely clearing it of any enemies, once one spawns the player will hear a siren sound alerting them of a Jackal spawning on the floor. The time it takes for them to spawn differs depending on a timer that the player can not see themselves, unfortunately the timer does not reset once you change floors which can lead to one of the Jackals to spawn almost instantly after clearing the room. The longer you take after one Jackal spawns will lead to a second one spawning and, of course, take too long with two of the Jackals on the floor the third will then spawn. The Jackals are level 200 each with superior weapons and armor that most players will not be able to even make a scratch into their health while the Jackals then can one hit kill most players.
Strategy
If you're still a fresh player with low tier fighters as well as low tier weapons and armor the only strategy would be to run to the nearest escalator and elevator without being seen. If you are seen pay attention to your stamina, the Jackals won't run after you necessarily but instead teleport as close to you as possible meaning if you run out of stamina the Jackals will most likely teleport close enough behind to finish you off. Also be wary of what is known as the drop kick of death, when close to an elevator or escalator don't continue running and press X in panic because that's how you perform the dropkick move which can prove a fatal mistake. Take your time once you get close to an exit and don't panic.
Now if you're not a fresh player then you probably learned a strat to kill the Jackals at this point. I will break my professional writing and say that I myself have not beaten a Jackal but I have seen videos of players using a combination of mushrooms to take down the Jackals which seems to work as a pretty good strat. The mushrooms that seem to do good at fighting a Jackal would be using multiple Guardshrooms (Invincibility), using Transparungus (Invisibility), Slowmungus (Slows time), and Stingshrooms (Attack up 100% and Defense down 50%). Along with using any combination of those I've also seen someone use Fishy Fungus while fighting multiple Jackals since it causes Confusion and the Jackals will fight each other and gives you a chance to throw some hits in until it wears off. That's all I got for strats myself on fighting them, it's probably the strategy I'll use once I'm leveled up enough and it seems to work well.
Good luck to those who choose to fight and remember if you choose to flee don't feel bad about it, it's the best choice.
Jackal Z
The only female in the group whose past is shrouded in mystery. Her weapon loadout consists of a high energy yo yo that does superior damage to players.
Jackal X
Jackal X is a former gangster as well as a violent brute. Known also for being very short tempered and very skilled especially with his choice of weaponry. His high energy beam saber will make quick work of any player that comes across him.
Jackal Y
Jackal Y is a former hitman and can be described as the "cool guy" of the group. He favors his elegant beam gun that can home in on targets and of course, one hit players.