You can also find a Remembrance Crystal in a chest in the same room – however this is a one-time chest, so the only way to get more is to continue fighting Reckless enemies. And since this Heartless is in the Cavern of Remembrance, you’ll want to max out as many Drive Forms as possible (at least get the highest level of Glide).
Remembrance Crystal Farming
The Remembrance Crystal can only be dropped by one enemy: the Reckless Heartless, found in the Engine Room in the Cavern of Remembrance. It has a 12% chance to drop a Crystal upon defeat. You can increase those odds with Lucky Strike, and since you’ll likely be farming this enemy towards the mid-to-late game, you’ll have time to synthesize some Lucky Rings too. One other good thing about farming here is that these heartless immediately respawn once you leave the room. So you can clear out the Reckless in the Engine Room, then head back to the previous room (the Mineshaft) and immediately re-enter. You should have the same Reckless Heartless spawn right away. The hardest part about farming these crystals is probably just getting through Cavern of Remembrance in the first place.
Remembrance Crystal Uses
Remembrance Crystals are necessary materials for a few synthesis recipes. Most are pretty good too, so let’s have a look at what you can make: Shadow Archive – This accessory is a replica of the weapon Zexion uses. It can be equipped to any party member and offers +3 magic and +5 AP. You can synthesize it after defeating Zexion’s absent silhouette, and to create it you’ll need x1 Lost Illusion, x1 Manifest Illusion, x1 Remembrance Crystal, and x3 Serenity Gems. Shadow Archive+ – If you have a LV3 Moogle and an extra Serenity Crystal, then you can synthesize this upgraded version of the Shadow Archive, which adds the MP Rage ability. It requires all the same synthesis materials + x1 Serenity Crystal. Centurion – This staff, modelled after Lexaeus’ weapon, is Donald’s strongest weapon in terms of Strength. It’s packed with +13 strength and +3 magic. You can synthesize it only after defeating Lexaeus’ absent silhouette. For actual materials, you’ll need x1 Lost Illusion, x1 Remembrance Crystal, x3 Remembrance Gems, x5 Remembrance Stones, and x7 Remembrance Shards. Centurion+ – Just like the shadow archive, the Centurion can be upgraded by a LVL3 Moogle and a Serenity Crystal. This will add the ability Damage Control. Again this requires the exact same materials as the Centurion above, plus x1 Serenity Crystal. Serenity Crystal – Serenity crystals are extremely valuable synthesis ingredients. They’re used in so many recipes to upgrade heaps of weapons & accessories into their + forms – and sometimes to create totally new items entirely! To craft a new Serenity Crystal through synthesis is quite a feat, requiring a LVL8 Moogle and x1 Tranquility Crystal, x1 Remembrance Crystal, and x9 Bright Crystals. Manifest Illusion – Like with other + items, the Manifest Illusion is the upgrade to a Serenity Crystal. It’s also used in a lot of recipes – and to synthesize this you’ll need the same materials as the Serenity Crystal, but with an added Serenity Gem. Also worth noting that collecting all “Remembrance” Materials in KH2.5 will reward you with a Serenity Crystal.
Are These Worth Farming?
For starters, the Centurion and Shadow Archive are definitely worth the investment. Both are useful items and will give you an edge in battle – especially if you want to take Donald more towards brute force strength rather than magic. And those two recipes only require 1 Crystal each, so farming shouldn’t be too difficult if you just want those items. Now, if you’re desperate for more Serenity Crystals for upgrading your synthesis items, then it’s going to be in your best interest to try and grind at least a couple more Remembrance Crystals. That said, there are other ways to obtain more Serenity Crystals aside from synthesizing them. But their recipe only needs x1 Remembrance Crystal each, so it’s not too crazy. In that scenario I’d say it’s really up to you to decide how much you’d want to farm here.