Fortress Crab
Fortress Crab (フォートレスクラブ Fōtoresu Kurabu) is an event-exclusive Raid Boss which can be fought in Kingdom Hearts Unchained χ / Union χ. Fortress Crab can be encountered if a Raid Boss is triggered while playing the event quest 2016 Showdown! Daily Raid Event on Thursday.
Fortress Crab Ω (フォートレスクラブ亜種 Fōtoresu Kurabu Ashu, lit. "Fortress Crab Subspecies") can be encountered if a Raid Boss is triggered while playing the event quests Raid Level: Legendary! Don't go alone!, Raid Level: Legendary! Don't Go Alone! during August 2016, Legendary Raid Level: Don't Go Alone! during March, 2017, Legendary Raid Level: Don't Go Alone! during September, 2017, and Legendary Raid Level: Don't Go Alone! during March, 2018.
Strategy
The Fortress Crab Ω starts at three million HP, however instead of the normal twenty minutes to defeat it, you get two hours.
The top node is 
Magic and is the least healthy, so destroy that first. The 
Power node (on the left) is the next weakest, followed by the 
Speed node (on the right).
Since you'll be using Power Medals to fight the Raid Boss, these nodes somewhat even out, but go for what you can stun the fastest, depending on your strongest deck, relative to your unique, specific arsenal.
Each follow-up attack for this event only costs 1 AP, so it is quite possible to just spam normal attacks over and over to kill the Raid Boss, even with no party members helping you.
You get roughly 3,000 Lux per nodes stunned, but only a small amount for each attack. Therefore it is highly recommended, due to the time given to kill it, to allow the nodes to revive as often as possible, to get the most Lux out of the Raid Boss.
Weekend Raid Event
As of August 6, 2016 there are now weekend only Raid Boss quests that will summon a Fortress Crab Ω. However, unlike the last Raid Boss event, these Fortress Crab Ω's start at ten million HP instead of three. You still only have two hours to kill it, but as long as you have party members helping you and you don't bother to wait for the nodes to revive, you can kill the Raid Boss within two hours.
You only have to kill three Fortress Crab Ω's in order to get enough Raid Coins to complete the event board, or two if you are the MVP or host for both of them.
Attack Prize Plus is beneficial for maintaining full Special Attack Gauges.
Like in the last event, you still get the most Lux out of waiting for the nodes to revive. However, the crab cannot be killed if the nodes are allowed to revive each time they are defeated, so try to weaken the crab to one million HP before farming it for Lux.
As of March 3, 2018, the Fortress Crab Ω now has 150 million HP, and the window to slay it has been raised to three hours. 740 coins are now needed to complete the weekend raid board, so defeating seven of one's own raid bosses and tapping the raid boss of a fellow party member's raid boss (or any permutation that leads to the sum total of 740 coins), are now the amount that's required.
One could enter with a triple-attribute hybrid KeyBlade (i.e. Starlight, Stroke of Midnight, or Fairy Stars), in order to first stun all three of the raid boss' nodes, before dying and returning with either a pure Power KeyBlade deck (i.e. Treasure Trove, Fenrir, or Darkgnaw), or Ignore-Attribute medals on their hybrid-attribute KeyBlades, to finish it off.
Double Lux/Half AP
There are four double Lux time periods for this event. Due to Daylight Saving Time changeover on March 12 at 2:00 am (PT)/9:00 (UTC), the double Lux periods will be on a different UTC time:
| PT | UTC (Before Daylight Saving) |
UTC (After Daylight Saving) |
|---|---|---|
| 2:00 - 3:00 am | 10:00 - 11:00 | 9:00 - 10:00 |
| 8:00 - 9:00 am | 16:00 - 17:00 | 15:00 - 16:00 |
| 2:00 - 3:00 pm | 22:00 - 23:00 | 21:00 - 22:00 |
| 8:00 - 9:00 pm | 4:00 - 5:00 | 3:00 - 4:00 |
There are three double Lux time periods for this event:
| PST | UTC |
|---|---|
| 1:00 - 2:00 pm | 20:00 - 21:00 |
| 5:00 - 6:00 pm | 00:00 - 01:00 |
| 8:00 - 9:00 pm | 03:00 - 04:00 |
Drops
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 14 |
Event Coins x100 |
Event Coins x100 |
Event Coins x100 |
| 15 - 49 |
Event Coins x200 |
Event Coins x200 |
Event Coins x200 |
| 50 - 99 |
Event Coins x600 |
Event Coins x600 |
Event Coins x600 |
Omega Drops
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 9 | Raid Coins x60 | Raid Coins x20 | Raid Coins x20 |
| 10 | 6★ Chip x1 | 6★ Moogle x1 | 6★ Dale x1 |
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 9 | Raid Coins x60 | Raid Coins x20 | Raid Coins x20 |
| 10 | 6★ Chip x1 | 6★ Moogle x1 | 6★ Dale x1 |
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 9 | Raid Coins x50 | Raid Coins x10 | Raid Coins x10 |
| 10 | 6★ Chip x1 | 6★ Moogle x1 | 6★ Dale x1 |
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 10 | Raid Coins x50 | Raid Coins x10 | Raid Coins x10 |
| Levels | Victory | MVP/Host | All Points Defeated |
|---|---|---|---|
| 1 - 10 | Event Coins x200 | Event Coins x100 | Event Coins x100 |