Mega-Potion

The Mega-Potion is a recurring item introduced in Kingdom Hearts that restores HP. In the first game, it restores 30 HP for each party member, while in the second game it restores 40% of the entire party's HP. In both games, it can be equipped for use in battle. In Kingdom Hearts Chain of Memories and Kingdom Hearts Re:Chain of Memories, it quickly restores all attack cards and resets the reload counter. In Kingdom Hearts 358/2 Days, it heals 40% HP to all players in the same map.

Kingdom Hearts
Mega-Potion can be synthesized once the second list is unlocked.
 * 1 Blaze Gem
 * 1 Frost Gem
 * 1 Thunder Gem
 * 2 Mythril Shard

Kingdom Hearts Final Mix
Mega-Potion can be synthesized once the first list is unlocked.
 * 1 Spirit Shard
 * 1 Power Shard
 * 4 Mythril Shard

Kingdom Hearts II
The Mega-Recipe used to create them is found in Beast's Castle in Beast's Room.
 * 3 Mythril Shard
 * 1 Power Shard
 * 1 Blazing Shard
 * 1 Lucid Shard

Kingdom Hearts 358/2 Days
The Mega-Potion can be synthesized for 1500 munny once Roxas is promoted to Novice rank.
 * 2 Hi-Potion

Kingdom Hearts III
Mega-Potion can be synthesized once 12 different synthesis materials are obtained.
 * 3 Lucid Shard
 * 3 Soothing Shard
 * 3 Pulsing Shard
 * 1 Hungry Stone

Kingdom Hearts

 * Mega-Potion: Air Pirate (1%), Aquatank (4%), Small Cannons at the End of the World (5%), Pirate (1%), Search Ghost (1%), AntiSora (40%), Shadow (10%), Shark (30%), Stealth Sneak (100%), and Wight Knight (0.5%).

Kingdom Hearts II

 * Mega-Potion: Morning Star (5%)

Kingdom Hearts Birth by Sleep

 * Mega-Potion: Blobmob (25%/49%), Bruiser (25%), Vile Phial (25%/35%)

Kingdom Hearts 3D: Dream Drop Distance

 * Mega-Potion: Skelterwild (2%)

Kingdom Hearts

 * Mega-Potion: Talk to Aerith in the First District after fighting Leon in Traverse Town; give a potion to a rose in the Lotus Forest at Wonderland; in a chest at the Coliseum Gates at Olympus Coliseum; three chests in Deep Jungle: one in the Treehouse, the Hippo's Lagoon, and in the Cliff area; four chests in Agrabah: two chests in the Plaza, a chest in the Alley, and in the Bottomless Hall; two chests in Atlantica: one in the Undersea Gardens area, and the other in Ariel's Grotto; using the Blue Trinity Mark in the Dungeon at Hollow Bastion; and a chest in the Library at Hollow Bastion.

Kingdom Hearts Birth by Sleep

 * Mega-Potion (Terra): A chest at the Purification Facility at the Radiant Garden; a chest in the Gizmo Gallery in Disney Town; a chest at the Coliseum Gates at Olympus Coliseum; a chest in the Turo Prison Block, and a chest in the Ship Hub in Deep Space; a chest along the Cliff Path in Neverland; and a chest in the Twister Trench at the Keyblade Graveyard.
 * Mega-Potion (Ventus): Two chests in the Gizmo Gallery in Disney Town; a chest at the Coliseum Gates at Olympus Coliseum; a chest in the Machinery Bay Access in Deep Space; a chest in the Cove in Neverland; and two chests at the Keyblade Graveyard, the first in the Seat of War, the other in the Twister Trench.
 * Mega-Potion (Aqua): Two chests in the Gizmo Gallery in Disney Town; a chest at the Coliseum Gates at Olympus Coliseum; a chest in the Turo Prison Block, and a chest in the Ship Hub in Deep Space; a chest in the Gully at Neverland; and two chests at the Keyblade Graveyard, the first in the Seat of War, the other in the Twister Trench.

Kingdom Hearts 3D: Dream Drop Distance

 * Mega-Potion (Sora): chest at the Training Yard; chest at the Grand Lobby; chest at the Cloudwalk; chest at the Glen; chest at the Fields.
 * Mega-Potion (Riku): chest at the Grand Lobby; chest at the Backstage; chest at the Machine Room; chest at the Moonlight Wood; chest at the Golden Wood; chest at the Fact within Fiction.

Kingdom Hearts III

 * Mega-Potion: Photograph 3 Lucky Emblems.

Kingdom Hearts 3D: Dream Drop Distance

 * Sora and Riku can purchase a Mega-Potion from the Drak Quack Ability Link for 25 Link Points.
 * Sora and Riku can purchase a Mega-Potion from the Ducky Goose Ability Link for 25 Link Points.

Notes and references
Mégapotion Mega-Potion