Abigail's Flower is a character-specific item used by Wendy to summon the Ghost of her twin sister, Abigail, by placing it on the ground and killing any Mob near the flower. Wendy's own death is also enough to summon Abigail. However, "murdering" a captured mob creature (Rabbit, Butterfly, Bee) directly from the inventory does not work as a sacrifice.
Mobs engaging each other and causing a mob death near the flower (e.g., Pigs vs Spiders ) can also cause Abigail to spawn. However, if Abigail "dies" and despawns into a flower and mobs die (or Wendy kills something) around the flower after the cooldown period, Abigail will not spawn unless the flower is picked up first and then placed down near a death occurring.
Summoning Abigail drains Sanity by 50 points. When she "dies", she will drop the flower so Wendy can spawn her again after the cooldown period has expired. Note that one hit from the player will kill her and she can often be targeted unexpectedly by the player during battle.
The flower has three stages of blooming. Initially, it will start as a pale, closed flower. Once charged, it becomes a more reddish pink color and is in bloom. In the third stage, when ready for the blood sacrifice, it will levitate slightly above the ground. Abigail's flower does not need to be in the player's inventory to bloom, so it may be left at the player's base in lieu of inventory space while it (re-)charges. Abigail's flower is also visible from the map screen, making it easy to relocate should the player accidentally lose track of it. If the flower somehow falls into the ocean, it will disappear as a normal item will and re-spawn near the player.
In situations where Abigail somehow ends up following a player character other than Wendy (e.g. by completing an Adventure Mode run), Abigail will continue to follow the new character around in Sandbox Mode but will not drop the flower upon dying.
In Don't Starve Together, Abigail's Flower can now be crafted from 6 Petals and a Nightmare Fuel. It is located under the Magic Tab. In addition to deaths of monsters and animals, the death of another player can also trigger the flower to spawn Abigail. If another player picks up Abigail's Flower, it will be reset to its first blooming stage. When left too long on the ground, Abigail's Flower may turn into a regular Flower.