From WiKirby, your independent source of Kirby knowledge.
Poison fruit is a term used to refer to certain poisonous objects dropped by Whispy Woods and his relatives. Unlike Apples and most other objects, these fruit may be dangerous to inhale, causing Kirby to take a small amount of damage when doing so, and being unable to spit them back out again afterward. Despite this, poison fruit can be destroyed by other means without consequence.
Kirby & The Amazing Mirror
Poisonous apples first appeared in Kirby & The Amazing Mirror, summoned as an attack by the Boss Wiz. They roll toward Kirby and stun him with the Sleep ability if he happens to swallow one.
Kirby Super Star Ultra
Poison fruit appear in this game as Poison Apples. These are occasionally dropped by Whispy's Revenge in Revenge of the King and The True Arena. They can be distinguished from regular apples by their purple coloration.
Kirby's Return to Dream Land
Purple poisoned apples can be dropped by Whispy Woods EX in both the Extra Mode and in The True Arena.
Kirby Star Allies
Poison cherries are among the objects Yggy Woods can drop.
The cherries dropped by Yggy Woods are (nearly) all poisonous to eat. However, these can be spat back out instead of swallowed to avoid the damage.