There are only two ways to farm Megalixirs: through synthesis or by juggling Rare Truffles. That’s it! As you’d expect, these items are exceedingly rare. So you’ll have to earn each one you get.
Method One – Synthesis
Megalixirs can be made in the Moogle Shop after creating 21 other unique items (they need to have ‘Mix’ next to their name). Once unlocked, a Megalixir can be synthed using the following items:
5x Lucid Gems 3x Lucid Crystals 2x Gale 1x Dark Matter
Lucid Gems: dropped by Gargoyles and Wight Knight s, which are easily found in Halloween Town’s Graveyard and Manor Ruins. Bambi can also drop them if he’s summoned inside Monstro. You’ll have to fill his gauge with three full bars (the maximum) for a 30% chance of a Lucid Gem dropping. Lucid Crystals: dropped by Darkballs, which appear all over the place. The easiest place to find them is in Traverse Town’s Second District. Bambi also has a chance to drop one when summoned in Hollow Bastion and has his gauge charged three times. Gales: dropped by both Invisible and Angel Star heartless, both of which can be found in the Linked Worlds area of the final dungeon. Dark Matter: can be found in various chests and as rewards throughout the game. They can also be synthesized using 9 Lucid Shards, 1 Gale, and 2 Mythrils.
Method 2 – Rare Truffles
The other way to get Megalixirs is by juggling Rare Truffles. When you juggle it one hundred times in a row you get a Megalixir! You can find these blue boys in the following locations:
Monstro – Throat Halloween – Town Bridge Neverland – Ship’s Deck End of the World – Final Rest
This method, of course, is easier said than done. But you can help yourself by going to Neverland to attempt it. Since you can fly there, it’s a lot easier to keep track of the truffle. And continuously smacking it vertically is pretty simple once you get the timing down.
Are These Worth Farming?
I don’t think so. Regular Elixirs are easier to find and they’re just as good, especially if you stock everybody up. Furthermore, you’re bound to come across a fair few Megalixirs anyway in your adventures, especially if you’re out grinding materials for all the synth stuff (and the Ultima Weapon). I wouldn’t go out of my way to farm for Megalixirs. It’s a lot of hassle and ultimately, you’ll get a lot of them anyway just through natural progression.