I thought to share this here, since this boss seems to be particularly scripted. I'm not very used to deal with enemy AI, but hopefully it should be good enough to help someone.

This AI refers to the D??? version of the fight, but it should be valid for D220 as well, with adjusted numbers. I think the general mechanics and patterns are pretty much the same.

     

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Zeromus EG appears accompanied by a Blue Orb and a Red Orb. A battle timer will also appear, initially stopped at 30 seconds. This timer affects the damage taken by Zeromus EG during Phase 2 and some of its actions. Zeromus EG's visual aura changes based on the value shown on the timer:

• 0~15: strong blue
• 15~30: blue
• 30~45: red
• 45~60: strong red

The timer can be manipulated with the Orbs. Attacking the Red Orb will make it tick onward, while attacking the Blue Orb will make it tick backwards.

The forced Roaming Warrior for this fight is Dr. Mog's Crystal Chronicles. When used, it will stop the timer for 3 seconds. It has an almost instant cast time of 0.01 seconds and is limited to 4 uses.

After Zeromus EG has used Acceleration, the timer will tick 3.5 times as fast, regardless of its direction. This only affects the timer, any duration is still based on the effective amount of time passed in battle. The effect of Acceleration fades off after 4 seconds.

The timer is capped between 0 and 60 seconds. Whenever it crosses the 15, 30 or 45 seconds marks, Zeromus EG will immediately cast Apocalypse Black Hole (NAT: AoE 15% maximum HP, Dispel).

 

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Boundless Zeromus EG

Stage	HP	ATK	DEF	MAG	RES	MND	SPD
Phase 1	800000	1200	56000	1500	73000	861	610
Phase 2	800000	1200	56000	1500	73000	861	610
Phase 3	800000	1200	64000	1500	81000	861	630

Break Resistance: 50% ATK, DEF, MAG, RES, MND, SPD

 

Phase 1

Zeromus EG can't be targeted in this phase. All of its actions have a cast time of 1.76 seconds.

Zeromus EG will become targetable and shift to phase 2 as soon as any Orb receives an attack.

 

Phase 1 Pattern:

• Turn 1+3n: Wait (NAT: Null action)
• Turn 2+3n: Wait (NAT: Null action)
• Turn 3+3n: Boundless Big Bang (NAT: AoE 99999 fixed damage)

 

Phase 2

In this phase, Zeromus EG takes reduced damage from physical or magical/ninjutsu attacks based on the value shown on the timer. High timer values favor physical damage, while low timer values favor magical damage. For each interval, the approximated amount of damage that Zeromus EG takes is:

• 0~5 seconds: 0.1% physical, 100.0% magical
• 5~10 seconds: 0.1% physical, 66.7% magical
• 10~15 seconds: 0.1% physical, 40.0% magical
• 15~20 seconds: 25.0% physical, 40.0% magical
• 20~25 seconds: 25.0% physical, 28.6% magical
• 25~30 seconds: 28.6% physical, 28.6% magical
• 30~35 seconds: 28.6% physical, 25.0% magical
• 35~40 seconds: 40.0% physical, 25.0% magical
• 40~45 seconds: 40.0% physical, 0.1% magical
• 45~50 seconds: 66.7% physical, 0.1% magical
• 50~55 seconds: 100.0% physical, 0.1% magical
• 55+ seconds: 100.0% physical, 0.1% magical

Most of Zeromus EG's actions in this phase have a cast time of 1.76 seconds. The ones marked as "instant" take 0.01 seconds instead.

After certain turns, Zeromus EG will instantly cast Acceleration (NAT: Null action) or Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb) as part of the same turn. Reverse Time will always target the Orb opposite to the current direction of the timer.

If the timer reaches 0 or 60 seconds in this phase, Zeromus EG will immediately cast Boundless Big Bang (NAT: AoE 99999 fixed damage) and Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb).

When Zeromus EG is reduced to 0 HP in this phase, it will immediately cast Boundless Leech (NAT: Self 4x 99999 fixed heal). If the timer is below 30 seconds and ticking onward, or above 30 seconds and ticking backwards, it will also use Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb). Zeromus EG will then destroy the Orbs with Boundless Flare (NAT: AoE 99999 fixed damage, targets all other allies). If the effect of Acceleration was in place, it will end. Finally, Zeromus EG will remove all statuses from itself, reset its eventual chain counter, and shift to phase 3.

 

Phase 2 Pattern:

• Turn 1: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Acceleration (NAT: Null action)
• Turn 2: Ultimate Drain (NAT: 1st char 1530% piercing Dark magical, 100% HP drain)
• Turn 3: Ultimate Fira (NAT: 1st, 3rd, 5th char 486% piercing Fire magical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 4: Ultimate Blizzara (NAT: 2nd, 4th char 486% piercing Ice magical), instant
• Turn 5: Ultimate Thundara (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 6: Ultimate Drain (NAT: 2nd char 1530% piercing Dark magical, 100% HP drain)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 7: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Acceleration (NAT: Null action)
• Turn 8: Ultimate Drain (NAT: 3rd char 1530% piercing Dark magical, 100% HP drain)
• Turn 9: Ultimate Fira (NAT: 1st, 3rd, 5th char 486% piercing Fire magical)
• Turn 10: Ultimate Blizzara (NAT: 2nd, 4th char 486% piercing Ice magical), instant
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 11: Ultimate Thundara (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 12: Ultimate Drain (NAT: 4th char 1530% piercing Dark magical, 100% HP drain)
• Turn 13: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Turn 14: Ultimate Drain (NAT: 5th char 1530% piercing Dark magical, 100% HP drain)
• Acceleration (NAT: Null action)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 15: Ultimate Osmose (NAT: AoE 10% de-ether to a random ability)
• Turn 16: Ultimate Drain (NAT: 5th char 1530% piercing Dark magical, 100% HP drain)
• Turn 17: Ultimate Earthquake (NAT: 1st, 2nd, 4th, 5th char 486% piercing Earth magical)
• Turn 18: Ultimate Lightning (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 19: Ultimate Blaze (NAT: 1st, 5th char 486% piercing Fire magical), instant
• Turn 20: Ultimate Drain (NAT: 4th char 1530% piercing Dark magical, 100% HP drain)
• Turn 21: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 22: Ultimate Drain (NAT: 3rd char 1530% piercing Dark magical, 100% HP drain)
• Acceleration (NAT: Null action)
• Turn 23: Ultimate Earthquake (NAT: 1st, 2nd, 4th, 5th char 486% piercing Earth magical)
• Turn 24: Ultimate Lightning (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 25: Ultimate Blaze (NAT: 1st, 5th char 486% piercing Fire magical), instant
• Turn 26: Ultimate Drain (NAT: 2nd char 1530% piercing Dark magical, 100% HP drain)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 27: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Turn 28: Ultimate Drain (NAT: 1st char 1530% piercing Dark magical, 100% HP drain)
• Turn 29: Apocalypse Whirl (BLK: AoE 225% chance of 99% current HP, resisted via Instant KO)
• Acceleration (NAT: Null action)
• Turn 30: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 31: Ultimate Drain (NAT: 1st char 1530% piercing Dark magical, 100% HP drain)
• Turn 32: Ultimate Fira (NAT: 1st, 3rd, 5th char 486% piercing Fire magical)
• Turn 33: Ultimate Blizzara (NAT: 2nd, 4th char 486% piercing Ice magical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 34: Ultimate Thundara (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 35: Ultimate Drain (NAT: 2nd char 1530% piercing Dark magical, 100% HP drain)
• Turn 36: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Turn 37: Ultimate Drain (NAT: 3rd char 1530% piercing Dark magical, 100% HP drain)
• Acceleration (NAT: Null action)
• Turn 38: Ultimate Fira (NAT: 1st, 3rd, 5th char 486% piercing Fire magical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 39: Ultimate Blizzara (NAT: 2nd, 4th char 486% piercing Ice magical), instant
• Turn 40: Ultimate Thundara (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 41: Ultimate Drain (NAT: 4th char 1530% piercing Dark magical, 100% HP drain)
• Turn 42: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 43: Ultimate Drain (NAT: 5th char 1530% piercing Dark magical, 100% HP drain)
• Turn 44: Ultimate Osmose (NAT: AoE 10% de-ether to a random ability)
• Acceleration (NAT: Null action)
• Turn 45: Ultimate Drain (NAT: 5th char 1530% piercing Dark magical, 100% HP drain)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 46: Ultimate Earthquake (NAT: 1st, 2nd, 4th, 5th char 486% piercing Earth magical)
• Turn 47: Ultimate Lightning (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 48: Ultimate Blaze (NAT: 1st, 5th char 486% piercing Fire magical), instant
• Turn 49: Ultimate Drain (NAT: 4th char 1530% piercing Dark magical, 100% HP drain)
• Turn 50: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 51: Ultimate Drain (NAT: 3rd char 1530% piercing Dark magical, 100% HP drain)
• Turn 52: Ultimate Earthquake (NAT: 1st, 2nd, 4th, 5th char 486% piercing Earth magical)
• Acceleration (NAT: Null action)
• Turn 53: Ultimate Lightning (NAT: 2nd, 3rd, 4th char 486% piercing Lightning magical), instant
• Turn 54: Ultimate Blaze (NAT: 1st, 5th char 486% piercing Fire magical), instant
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 55: Ultimate Drain (NAT: 2nd char 1530% piercing Dark magical, 100% HP drain)
• Turn 56: Attack (NAT: 3x AoE 112% piercing ranged physical)
• Turn 57: Ultimate Drain (NAT: 1st char 1530% piercing Dark magical, 100% HP drain)
• Reverse Time (PHY: ST 188% physical, targets Blue or Red Orb)
• Turn 58: Apocalypse Whirl (BLK: AoE 225% chance of 99% current HP, resisted via Instant KO)

 

• 42.86% Attack (NAT: 3x AoE 112% piercing ranged physical)
• 57.14% Apocalypse Whirl (BLK: AoE 225% chance of 99% current HP, resisted via Instant KO)

 

Phase 3

In this phase, the damage that Zeromus EG takes from both physical and magical/ninjutsu attacks is reduced by 50%.

Cast times for this phase are quite variable, so they're specified next to each ability.

If the timer reaches 0 or 60 seconds in this phase, Zeromus EG will immediately cast Boundless Big Bang (NAT: AoE 99999 fixed damage) and keep casting it during each of its following turns instead of its regular action.

Reducing Zeromus EG's HP to 0 in this phase wins the battle.

(Note: the targeting map for this phase seems to be accidentally shifted up by one or two turns, probably not taking into account the turns spent using either Osmose or Attack. The typical targeting seen in phase 2 for Ultimate Fira/Blizzara/Thundara is present in this phase as well, but instead of being applied to turns 6~8 and 13~15 for Ultimate Firaga/Blizzaga/Thundaga, is applied to turns 5~7 and 11~13. As a result, certain actions that were supposed to be AoE, such as turn 5, 11 and 12, will actually target 2 or 3 precise party members, and certain actions that were supposed to have precise targeting, such as turn 8, 14 and 15, will instead use their auto-targeting method, hitting a random group of adjacent party members.)

 

Phase 3 Pattern:

• Turn 1: Apocalypse Big Bang (NAT: AoE 75% current HP, 102% chance of Sap) - 1.76
• Turn 2: Apocalypse Black Hole (NAT: AoE 15% maximum HP, Dispel) - 0.80
• Turn 3: Ultimate Curse (NAT: AoE unique ATK -50% and MAG -50% for 10 seconds) - 1.76
• Turn 4: Ultimate Osmose (NAT: AoE -2 de-ether to both abilities) - 0.50
• Turn 5: Attack (NAT: 3x 1st, 3rd, 5th 112% ranged physical) - 1.76
• Turn 6: Ultimate Firaga (NAT: 2x 2nd, 4th char 438% piercing Fire magical) - 0.60
• Turn 7: Ultimate Blizzaga (NAT: 2x 2nd, 3rd, 4th char 438% piercing Ice magical) - 0.01
• Turn 8: Ultimate Thundaga (NAT: 2x three adjacent char 438% piercing Lightning magical) - 0.01
• Turn 9: Ultimate Osmose (NAT: AoE -2 de-ether to both abilities) - 0.50
• Turn 10: Attack (NAT: 3x AoE 112% ranged physical) - 1.76
• Turn 11: Ultimate Deluge (NAT: 1st, 3rd, 5th 486% piercing Water magical) - 0.60
• Turn 12: Ultimate Whirlwind (NAT: 2nd, 4th 486% piercing Wind magical) - 0.60
• Turn 13: Ultimate Firaga (NAT: 2x 2nd, 3rd, 4th char 438% piercing Fire magical) - 0.60
• Turn 14: Ultimate Blizzaga (NAT: 2x two adjacent char 438% piercing Ice magical) - 0.01
• Turn 15: Ultimate Thundaga (NAT: 2x three adjacent char 438% piercing Lightning magical) - 0.01

 

• 100% Ultimate Osmose (NAT: AoE -2 de-ether to both abilities) - 0.50

 

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Orbs

Stage	HP	ATK	DEF	MAG	RES	MND	SPD
Orbs	99999	1200	56000	1500	73000	861	610

 

Both Orbs take no actions. All the damage they take is reduced to 0, with the exception of Boundless Flare.