Megalixir

The Megalixir is a rare healing item that recurs throughout the  series. It can typically be used in battle to fully restore HP and MP to all party members.

Mechanics
In Kingdom Hearts, Kingdom Hearts II, and Kingdom Hearts III, a Megalixir fully restores the HP and MP of all party members.

In Kingdom Hearts Chain of Memories, Megalixir is an item card that instantly restores all attack cards and magic cards that have been used, including those lost through sleights, and resets the reload counter. The Megalixir card is required for the Holy sleight.

In Kingdom Hearts 358/2 Days, Megalixir is an item panel that fully restores the HP and all magic casts of every party member.

In Kingdom Hearts Birth by Sleep, Megalixir is an that fully restores the user's HP, Focus Gauge, and D-Link Gauge; and eliminates any negative status effects. One slot in the Command Deck can hold two Megalixirs.

In Kingdom Hearts Re:coded, Megalixir is an that fully restores Data-Sora's HP, eliminates any negative status effects, and raises the clock level to MAX. One slot in the Command Deck can hold one Megalixir, with a memory consumption of 12%.

In Kingdom Hearts 3D: Dream Drop Distance, Megalixir is an that fully restores the HP of all party members, charges all Link Gauges and command gauges, resets the Drop Gauge, and eliminates any negative status effects. One slot in the Command Deck can hold two Megalixirs.

Kingdom Hearts

 * Megalixir: Rare Truffle (100 Hits)

Kingdom Hearts Birth by Sleep

 * Megalixir: Hareraiser (1%)

Kingdom Hearts

 * Megalixir: Chest in Aladdin's House, chest at Rising Falls, Blue Trinity in Great Crest, chest at World Terminus, chest at Final Rest.

Kingdom Hearts Chain of Memories

 * Megalixir: Room of Rewards (set 1) in Destiny Islands.

Kingdom Hearts Birth by Sleep

 * Megalixir (Terra): Chest at the Rainbow Falls: Base; chest at Skull Rock: Cavern; chest at the Twister Trench.
 * Megalixir (Ventus): Chest at the Rainbow Falls: Base; chest at the Cove; chest at the Twister Trench.
 * Megalixir (Aqua): Chest at the Mysterious Tower; chest at the Twister Trench.

Kingdom Hearts 0.2 Birth by Sleep -A fragmentary passage-

 * Megalixir: Chest at The World Within.

Kingdom Hearts III

 * Megalixir: Chest at the Breezy Quarter.

Kingdom Hearts 358/2 Days

 * Roxas can redeem five Megalixirs once 120 Mission Crowns have been obtained.

Kingdom Hearts 3D: Dream Drop Distance

 * Sora and Riku can purchase a Megalixir from the Drak Quack Ability Link for 50 Link Points.
 * Sora and Riku can purchase a Megalixir from the R & R Seal Ability Link for 100 Link Points.

Kingdom Hearts III

 * Sora is awarded a Megalixir from putting Olaf back together again after completing Arendelle initially.

Notes and references
Mégalixir Final-Elixier