The Hydra Headstone is a temporary event building and special edition decoration in Clash of Clans, introduced during the Mashup Mania event in October 2024. It was available for free after completing the main reward track by collecting 16,000 Sour Elixir awards players with the Hydra Headstone decoration, which features a spooky head with glowing horns and eyes floating above a sour elixir pool. This cosmetic item can be placed in the home village to add a sinister Halloween aesthetic, though the building itself is only available for the duration of the specific event.