Undead Bait is actually a "miracle tonic" that was peddled by Nigel West Dickens in Fort Mercer as being able to cure and prevent the Undead Plague as well as a function to repel and ward off the Undead. However, it actually attracts the Undead. This can be used towards the player's advantage by throwing a bottle of Undead Bait to attract any Undead to the spot where the bottle landed, enabling the player to make a hasty escape, nail some headshots, or blow the amassed horde to smithereens with Dynamite.
Undead Bait is given to the player during the mission "A Cure for Most of What Ails You". According to Nigel West Dickens, it was a cure for the infection. However, after witnessing a man who drank the tonic get brutally mauled by a crowd of Undead when trying to test the false repelling effects, West Dickens decided the tonic would prove more useful as a bait to attract the Undead.
Although this is one of the weapons Marston can possess, players cannot "cheat" for it because its DLC.
Undead Bait can be built directly from the kit section of John's satchel with the "Build: Undead Bait" option. This uses up one Prairie Poppy and one Wild Feverfew to create a single bottle of Undead Bait, but upon 100% completion of Undead Nightmare, building Undead Bait will not spend any supplies.
Undead Bait is very useful in the multiplayer game mode Undead Overrun. It can be used to temporarily distract the horde when trying to revive another player, open a coffin, or flee from a horde that is a little too big. After the Undead Bait attracts a crowd, hurl a stick of dynamite or a bottle of Holy Water in the middle of the group to take out a large number of Undead. This makes it much easier to clear the wave. This yields an excellent kill chain as well, helping with the Zombie Kill Chain challenges.
Be careful not to run into the small cloud the bait creates, as your player will trip and act as if hit by a Fire Bottle. This disables the player temporarily right in the middle of the converging horde. Zombies will directly prioritize the cloud of bait over the fallen player if close enough, leading to certain death.
For some reason, if Undead Bait is thrown near a group of Undead it will cause them to fall on their backs. If NPCs move over the spot while riding a horse, the rider will be thrown from the back of the horse.
During the cutscene of the mission where the undead bait is introduced, the bait looks like a normal bottle of elixir; however, when John uses it as bait the bottle turns green.
If the player is lucky enough to hit an undead in the head with the bait, their head will explode. The bait will still have its effect on the area
Undead Bait has the ability to ricochet off water without its effect.
There is a glitch with Undead Bait. If you go into Dead Eye and mark a spot on a gatling gun, it will hit the gatling gun, but the bottle will be floating in the gatling gun for about seven or eight seconds. Then it will disappear. This also works with any other thrown weapon.
If Undead Bait is thrown to a human, it will either kill or damage the person that was caught in the area.