Considered as one of the Hardest bosses in Final Fantasy franchise. Bhunivelze+ in Chaos mode is not easy as Bhunivelze in normal mode or even the hard mode. This guide would discuss the Equipment and Strategies that can be used to defeat Bhunivelze+.
First things first- Bhunivelze + has roughly 103 Million HP and can only be accessed if you have gone to the Ultimate Lair in Hard Mode. He is defnitely not the same as Bhunivelze in normal mode at all. You can recognize him uniquely since he will remove his mask that is hiding his face. Bhunivelze+ however is vulnerable to Deprotect, Imperil and Deshell. Upon staggering this would sometimes be automatically attributed to him or you can choose to hit him with appropriate spells.
Don't kid yourself- you would need several runs in LR to beat him. For me it was 4 runs to at least get my -ra spells maxed out or to get it to level 5. Essential to get your Heavy Guard, Heavy Slash, Blitz to be maxed out as much as possible for this fight. You will also need a handful of ethers, turbo ethers, phoneix downs, x-potions to beat him. Ethers are mostly useful for taking his HP out when he is staggered. Elemental potions are a must in this fight if you want to stagger him fairly quickly and increase damage by physical attacks as well. And after staggering you need Bravery potions so that you can damage him a lot.
Anything that increases ATB recovery is important in this battle and can be found by defeating Aeronite (Falcon Charm --> ATB Speed 200) there is also Bandit scarf, etc. Essentially, maxing out debuffing abilities would give you ATB recovery as well. In terms of weapons, ,get one for maxed out magic and another for maxed out strength (5000 strength or magic if possible). Since staggering is a main priority in this fight- a weapon which can max out strength with a staggering capability (like Cloud's Buster Sword) is super useful. Inititally Chaos Revenge (Caius's sword) would have Quick stagger 75% which is super useful for this purpose.
Garb / Equipment
There are many Garb combos which would work but that depends on your overall strength and level. I will discuss most commonly preferable Garbs to make this fight be yours.
For this fight- you will absloutely need a perfect guard, this can be obtained by either defeating Ereshikigal in Ultimate Lair or getting the Garb Pallas Athena (which can only be taken after getting every single achievement in this game). This gives 99% physical and magical resistance. I suggest you to have this ability in one of your Garbs. But the downside is, this would consume extreme ATB and that mostly renders it useless.
The workaround for this is, using Sacred Knight Garb which would make your Heavy Guard (heavy guard with at least 70% magical and physical resistance) to Heavy Guard+ which would block any attack of God's with low ATB consumption except for unblockable attacks such as Hyper Nova.
Alternatively you can also create either a Garb (Cyber Jumpsuit or Guardian) which can be resistant to either magic or physical damage 99%. Since this would involve using accessories like Preta hood or Ghostly hood, this would greatly lower your magic or strength which would extend the fight very long but if you have fairly middle stats and not super powerful, this is probably your way to go. With this type of Garb blocking is unnecessary and you would be totally immune to either magical or physical attacks completely.
In terms of attacking, you can use Soldier of Peace, with a maxed out Heavy Slash. You can use accessories that would add like more power to your wind attribute attacks or other elements (such as Windwalker Bracelet) For the other Garb I commonly used Equilibrium+ which will hasten stand by recovery, but you can also use Martial Monk which has whirlwind kick which is another physically powerful Garb. Make sure that abilities, Imperil, Deprotect, Deshell and Blitz are equipped, Ruin is also useful in Bhunivelze's final form which only relies on staggering.
Phase 1 / 2
In Phase 1, God would mainly use -ra and -ga spells along with Monad Beget mostly. The player can start the fight with Imperil and then trying to stagger him using the -ra spells. He will change his spirit however he pleases (like from Fire to Aero) in this mode and this requires you to at least equip two different kinds of -ra spells. I recommend Aerora and Thundara since those are speedy.
Make sure you use your elemental potions to stagger him fast but keep in mind you will be attacking him using magic which is opposed to his spirit, so its useful to bring different elemental potions for a quicker fight. Using Sacred Knight or Heroic Guard all magic could be blocked. He would eventually summon the 4 balls which would have to be destroyed immediately (Monad Begnet) before God do Wings of Destruction which would instantly kill you or take half of your HP out even with perfect guarding. Blitz with a strength maxed out weapon could be used to attack them all at once and then individually soldier of peace could be used fast as well.
After a while God would try to cast Genethliac Hymn and this is players opportunity to stagger him. If not staggered he will use Fallen Star or Dancing Mad which is not blockable and is an Instant kill. When he is staggered just do your debuffing and take a bravery potion, use over clock with ethers and attack him in Soldier of Peace or your Attack Garb. Alternatively, you can use elemental potions and then physically attack as well but with the appropriate accessories. Don't elongate the fight or else he would also try using much harsher attacks such as Hyper Nova which is also an instant kill thats the whole purpose of using Overclock in this case.
PRO TIP: Using Martial Monk (Whirlwind Kick) and Soldier of Peace (Artemis Arrows) it is possible to interrupt Wings of Destruction even without destroying Monad Begets. If you are able to fully debuff him while being equipped with Forsaken Tie, Locket Pendant+ and Wind Walker bracelet plus drinking elemental potion would have a higher chance of doing this. However, you will need to be fast and practiced with your combos so as to not give God a chance to strike you (yikes). Thank for MasterLL for this tip.
If you don't take his HP out in the first phase fast enough, he will evolve into his physical attack phase (Phase 2) which can be a headache. One miss of guarding would be enough to kill you instantly. With a heroic guard or the Sacred Knight his attacks are utterly blockable and is a joke mostly. He will use two attacks : Divine Judgement which he would swing his sword at you 4 times and then cas a finishing blast. Then there is Almagest which is like a ray of energy which if you do not block it fast enough its instant death. Don't elongate this phase either and try to use Overclock and take his HP out after he is staggered. After his HP is over in these 1 or 2 stages he will go to his Final Phase.
This phase is all about staggering him, and this is where Ruin is very handy. You can also use the attack ability Beat down to extend the stagger power. Spam all your -ra spells with ruin and beat down and after a while the stagger meter would render red. Do not panic because of the death countdown on you, because a single miss would get you killed in this phase as well (excluding the heartless angel which reduces HP to 1).
Staggering will take some time depending on your efficiency of Garbs and Recovery items etc. But it is possible to do it within the Doom count down. After he is staggered, get your best attack garb, drink a bravery potion and do your job using soldier of peace or Martial Monk, if you have ethers remaining use those as well. If you do not take all of his HP out when he is staggered in this mode, he will get up and spam a lot of high level spells which you should block immediately. Upon getting up again, god will again cast Doom on you and you should try continue to stagger him while guarding against his eye attacks and heartless angels like you did before and attack him with your attack garb when he is staggered.
He will drop Elementelaga and Crystal Malistones. In my opinion the rare weapon Double Deity can be obtained without 5 stars and if you finish the fight within 20 minutes or so. Just try killing god again and again the weapon would pop up (using the Autosave before killing him). Alternatively you can use the accessory Beggars Beads to enhance the drop out rate.
For me, this boss is far harder than both Ereshikigal and Aeronite of the dead dunes. As fearsome it is, it is not impossible to defeat him and it would take several tries to get used to anticipate his attacks and such. However, as the final boss of the finale of the FFXIII series Bhunivelze definitely took the limelight.