The Trial is infamous among the fanbase, due to rendering physical damage units useless, which comprise most of the meta. It is generally less frowned upon in the Global fanbase due to the availability of more Magic Damage units of high caliber.
Bloody Moon has 6,000,000 HP in ELT difficulty, but the battles play out similarly regardless. The Moon is immune to physical damage, so using them is ill advised. The Moon has two battle phases which determine its behavior in both of them the Moon will shift between Lunar Phases (New Moon, Half Moon, Full Moon and Crescent Moon rotation) which have different effects each. Regardless the Moon can attack up 12 times per turn.
The Moon has no elemental resistances, is immune to status ailments and resists all stat breaks.
The Moon will restore its HP back to full health every turn with its Lunar Phase abilities and will buff itself and the Apostles with defensive buffs (DEF and/or SPR buffs the magnitude of which depends on the phase). Every 3 turns it uses Total Eclipse for moderate Magic Damage on all units. The rest of the attacks are normal attacks with a 15% chance of them being Comet Moon (moderate Magic Damage on one unit).
This phase lasts until one of each Apostle is destroyed. The Moon will spawn one Apostle as soon as one of them is destroyed, the Moon always opens with 3 Apostles so if all of them are destroyed it will summon 3 new Apostles, followed by the last 2 ones.
As soon as the last Apostle is defeated the transition between phases will occur. This is one of the most dangerous parts of the fight as the Moon will use Scorn of the Moon for 100% KO on all units. Subsequently it will unleash its attacks on the party if any of them survive. During the transition the Moon restore its HP to 100% but it will behave as with whatever HP was when the phase changed (if below 90% it will summon an Apostle and if too low it may use a threshold attack). If the Moon is below 90% it will spawn one Apostle per turn (never of the same element).
The Moon's Lunar Phase is now different being upgraded to their Crimson versions. All of them inflict Moderate Magic Damage on all the party but there are differences: Crimson New Moon reduces DEF and SPR by 20% for one turn to all units. Crimson Half Moon reduces DEF by 20% for one turn to all units. Crimson Full Moon reduces ATK, DEF, MAG and SPR by 30% for one turn to all units. Finally Crimson Crescent Moon reduces SPR by 20% for one turn to all units.
At every threshold (each 20%), the Moon will use Moon Revolt which has differing effects initially believed to be related to the Moon Phase, however in truth the Moon Phase is irrelevant and the Moon goes through a procedural check in priority order until something happens, like this: 20% chance to remove one unit from battle for 4 turns -> 20% chance for strong physical damage on all units -> 20% chance 75% debuff on all stats to all units -> 10% Scorn of the Moon -> 100% chance for strong magic damage on all units. That is to say if the checks fail, the player is at the very least guaranteed to get assaulted by magic damage on each threshold.
Additionally, the Moon will retaliate Black Magic with an attack very similar to Moon Revolt (this one does depend on the Crimson Lunar Phase). If Black Magic is used and a threshold is crossed, then there will be twice the retaliation.
The Apostles have 500,000 HP in ELT difficulty and have much higher SPR than the Moon and also have a physical damage immunity. There are 8 Apostles one of each element. The Apostles can attack up to 5 times per turn and will open with strong Magic Attack to one unit of the element they are aligned with.
During Phase 1 the Aqua, Ice and Thunder Apostles are always the first to appear at the battle, followed by Flame, Earth, Wind, Light and Dark Apostles. Later on Phase 2 the Moon will spawn them once per turn at random until there are a total of 3 (never the same element). In Phase 1 the Moon will spawn as many Apostles until there are 3 (so long as there are elements left). In Phase 2 it will always spawn 1 per turn regardless of how many are destroyed until there are 3.
If the Moon is defeated but an Apostle is left alive, it will heavily retaliate by respawning other Apostles and then they will expel the player's units one by one with Kidnap resulting in a wipe. Therefore the Apostles and the Moon must be defeated on the same turn.
The Apostles have a 200% resistance to their own element and -2000% weakness to the opposite element. Are immune to all status ailments and have a 50% chance to be ATK/MAG broken.
The Battle has tricky perks, but it is largely considered to be significantly easier than The Rumble of Malboro, since there are far less things to pay attention to, making this battle difficult but far less obnoxious.
As detailed above, no physical damage will work so the player must use Magic Damage, but they must also avoid using Black Magic or the retaliation will likely be fatal. That leaves units with Magic Damage non-Spell abilities. Ashe is an accessible and powerful option which can reach high levels of MAG relatively easy and can provide on an additional healing. Two copies of Ashe can chain and provide healing and LB cryst/Esper Orb spawn which will be useful. The better options however are more difficult to acquire but will greatly benefit the player. Ace, Trance Terra or the time limited, global exclusive Grim Lord Sakura will be very helpful. The former two can deal great damage (especially so Trance Terra) when enhanced to their fullest, while Ace doubles as MP battery. Grim Lord Sakura is a very powerful Magic Chainer with very high HP values (provided she equips her Reaver) which also has other support abilities and she can chain with Ashe as well.
Even if the player uses double Ashe, a healer is recommended regardless. The usual, Refia, Tilith, Aria, Ayaka, Luka will work very well. Non Tilith/Ayaka units equipped with Dualcast or the Holy Wand from The Troubled Strategist will help magnificently (this item also comes with Holy for one of the missions).
A Tank is also recommended as the Bosses do employ physical attacks regularly and MAG units tend to be frail on DEF. Warrior of Light is useful with The Light is With Us! and with Arms Breaks against the Apostles. Veritas of the Earth can use Guardian for defense, Omni Block to resist the Moon's most powerful stat breaks and his Limit Burst, Demon Wall will help immensely at a higher level. With Magic chainers he should have a reasonable LB fill each turn.
Support units will be needed, be them buffers or MP Batteries as the battle can take a huge toll on MP. Soleil is a good buffer, Lunera doubles as MP Battery and mild buffer, Rikku can provide Reraise (which will most likely be needed).
The first phase isn't too difficult as the player will mostly deal with the Apostles while the Moon plays a more defensive roll. Using Magic Chains that strike all enemies is very helpful in dealing with them efficiently. Elementals can help but are not mandatory, plus neutral chains will allow the player to defeat many of them simultaneously without risks.
The Phase 1-2 transition is one of the most difficult parts of the battle. Due to the instant KO the player will need Reraise to keep battling, even if they survive it, the Moon will strike all of them completely deprived of any buff, sparking a death flag. There are however some tactics to survive easier. First the Moon should not be below 90% during the transition so as to avoid spawning an Apostle an additional attacks in a rather defenseless time. Secondly Anti-KO equipment like Safety Bit or Genji Shield will also help and they should be equipped on key units, for example Safety Bit on Rikku will likely guarantee she can revive KO units with Mega Phoenix, Genji Shield on Veritas of the Earth will allow him to Tank attacks and eventually use Demon Wall to help the resurrected units survive the following turn. Thirdly they should this transition in a Total Eclipse turn to avoid further problems.
After that the battle resumes as usual, but the player should pay attention to the Lunar Phase. They should aim for either Crimson Half Moon or Crimson Full Moon as a stat break can be survived and repelled with anti-break buffs, and Crimson Full Moon is as strong as Total Eclipse which can be survived. Crimson New Moon is a very strong physical attack which will likely result in a wipe or in severe casualties even with Reraise. Crimson Crescent Moon can expel key units from battle (albeit only temporarily and while the Moon is alive but 3 turns is still enough for the player to be overwhelmed).
As such the greatest difficulty of the battle lies on 3 points: a) Surviving the 1-2 Phase. b) Managing the thresholds. c) Destroying all enemies on the same turn. The last condition can be met much easier with a Bahamut Megaflare cap which on a proper chain can wipe the enemy party.
Strictly speaking all of Phase 2 can be bypassed since technically the Moon can be killed in Phase 1, provided the player can inflict over 6,000,000 damage. Proper buffs with at least two fully enhanced Trance Terras can achieve this. Bahamut can also help in achieving that.
Because the player can damage/kill the Moon at basically any time even if all enemies must be destroyed, it is the main reason why this trial is easier than Malboro's.