Plant Life: WoW Battle Pets

Vendor: Irisee

Zone: Icecrown

Cost: 40 (unlimited supply)

Pet Store 

Vendor: Ayla Shadowstorm

Zone: Molten Front

Cost: 1500 (unlimited supply)

Pet Battle: [1-2] Eversong Woods

Quest: Lawn of the Dead [20]

Zone: Hillsbrad Foothills

World Event: Hallow's End

Item: Crudely Wrapped Gift (obtained via daily Hallow's End quest)

Daily Instance: Headless Horseman [75+]

Drop Rate: 1 in 20 dropped (avg. all sources; available 15 days per year)

Vendor: Rook Hawkfist

Zone: Icecrown

Cost: 40 (unlimited supply)

Drop: World Drop

Zone: Valley of the Four Winds [86-90]

Pet Battle: [6-7] Wetlands

Achievement: That's a Lot of Pet Food

Category: Collect

Horde Vendor: Apothecary Furrows

Quest: Remembrance of Auberdine

Zone: Darkshore (unlimited supply)

Alliance Quest: Remembrance of Auberdine [15]