I'm still playing FFRK, and it's been a lot of fun, despite some of the wonky balance issues that pretty much necessitate the use of S/L tricks to reset the fight. As the game moves forward, you have power creep as you are wont to have in a mobile game, but the developers have started putting in extremely difficult fights that are FFRK at its best: a puzzle game with an execution phase.
There have been 3 of these "Ultimate" fights so far: Exdeath (FFV), Yunalesca (FFX), and Rubicante (FFIV).
Exdeath was a bit of a wake-up call for a lot of players. The ability to spam AoE magics, AoE physical attacks, and Dispel the entire party as a counter attack meant that while the standard Retaliate/Reflect strats were pretty well required, you also really needed a lot of mitigation. Stacking Shellga, Full Break, and Magic Breakdown reduced damage to tolerable levels (though it still required a lot of AoE healing). The fun part was that while he got twice the actions per round once he hit 50% health, because most of them turned into single-target mega-spells, suddenly you could just Carbuncle to reflect-all. The latter half of the fight was easier than the beginning of the fight.
Yunalesca was crazy easy, especially compared to her FFX counterpart which was probably one of the harder fights in the game. Retaliate was the name of the game here, and you'd pretty well rip through her in no time. Because of her Stage 3 Osmose spam pretty well reducing you to no ability uses left, Retaliate allowed your party to dish out impressive damage still.
Rubicante Ultimate, though, oh man, this required some impressive thinking to try and fight the mitigation required onto your team, deal with his gimmick, and still dish out enough damage to win, but quickly enough to keep taken damage low and kill him before your mitigation ran out. This fight really stressed having access to specific abilities that could only come from pulling certain gear.
The FFRK community on Reddit has determined there are 3 types of Soul Breaks (SBs)--super special attacks characters can learn from equipping gear, and can only be cast when your soul break bar has enough energy gained from taking damage/using actions--that are pretty much essential. Named the Holy Trinity of SBs, they are Wall, Medica, and Hastega (or Boostega).
The FFRK Holy Trinity
Wall is only on two characters currently: Tyro, and Y'shtola. And both of them require a very specific relic to learn said wall. But the effect is to raise the Defense and Resistance of all allies by 200% (!!!) for 25 seconds. This stacks on top of Shell/Protect, which both raise Resistance and Defense by 100%, so combined you're looking at a damage reduction of nearly 88% (since they stack multiplicatively), which makes this incredibly powerful.
Medica is basically any AoE heal (as they are only available via Soul Break). There are currently 19 Medicas in the game, of varying effectiveness. I have Y'shtola's and Vanille's, which are two of the most powerful ones available. On top of that, many Medicas have secondary effects. Vanille's also casts Protect as well as healing. Y'shtola's has an Esuna effect, both quite useful. I also have a "Shared" Soul Break from the armor "Mystery Veil" that cannot be learned, but a character can access while they have the item equipped, which has helped in a pinch as well.
Hastega/Boostega is generally a two-buff AoE Soul Break, generally one of which is Haste. You cannot get AoE Haste outside of these Soul Breaks, which is why it's so powerful. Currently there are only 3 Hastega Soul Breaks: one for Red XIII (Lunatic High, Protect/Haste); one for Sazh (Boon, Shell/Haste); and Eiko (Emerald Light, Medica/Haste). All three are incredibly useful, especially when you need to bring both Shellga and Protectga to a fight, saving you an ability slot.
Mitigation While Missing The Trinity
I'm a Day 1 player of FFRK, which means I have an impressive amount of gear and abilities. A really impressive amount. Yeah, I've spent probably about $100 on the game, but I've also played for 9 months, which works out to less than what I'm paying for WoW, so I'm okay with this. But even still, I'm missing Wall and Hastega from the Trinity. As mentioned, I have three Medicas (Y'shtola, Vanille, Mystery Veil), though only two of them are really fantastic.
Unmitigated on a character with ~250 Resistance, Rubicante dishes out ~5400 damage single target to a character. Most of my characters have 4000 health of so. Rubicante resists Breaks, so Magic Breakdown will "only" reduce that by about 41%, bringing each shot down to ~3,175 damage.
Shellga increases Resistance by 100%, so stacking those two brings him down to ~1,774 damage a shot, which is still not enough. He'd roast me well before I could heal my party. Even with two Medicas that heal the entire party for ~1,800, I can't spam them every round, so we need to reduce damage further.
So either I had to find a way to fit Full Break on my team, or I suck it up and use my "Wandering Record Warrior", AKA friend power, for 2 uses of Wall. This would mean that with Shellga, Wall, and Magic Breakdown, said attack would only do ~991 damage, well within healable range.
For funsies, Celes' default Soul Break, Magic Shield also boosts the party's Resistance by 50%, and is stackable, bringing us to a total of ~705 damage with all my possible mitigation up for the largest single target attack he can bring to bear. His AoE attack would only hit the party for ~423 damage.
So we can survive, and I'm pretty much obligated to bring Celes, Y'shtola, and Vanille, and a Wall for a friend, leaving me with 2 other characters to bring, but no Hastega.
Dealing With Mechanics and Dishing Damage
The next step was to fit someone on my team who could use Thief 4 abilties. Rubicante is weak to ice/water damage, but every 3 turns he'll put up his cloak, which makes him absorb those elements instead, and counter pretty much everything. Basically, when he cloaks, you're going to get wrecked.
However, you can force him to remove the cloak early by "stealing" from him, similar to the mechanic in the original FFIV game. In this case, your options are Steal Defense or Steal Power. Steal Power is the only that ups your own damage, and given most of my attacks are going to be magic since Rubicante counters physical attacks often, Steal Defense makes not much sense.
So now my party was:
Celes (Magic Caster)
Vanille (Magic Caster/Healer/Buffer/Whatever)
No Thief can use Full Break and Steal Power, so rather, I decided to use Spellblade for Watera Strike. That meant using Balthier, as he is the only current Thief 4 with Spellblade 3.
Which left us with a Magic Caster to bring. Since I had a fantastic weapon for Rydia, and she would get the Realm bonus, Rydia it was. For Celes I had a FFIV synergy 5* Ice Rod thanks to the earlier FFIV event loot that increased ice damage dealt, so she got all my ice spells, and Rydia got all my Water spells.
I still needed to fit Magic Breakdown, Shellga, a heal, and to deal with the fact I didn't have Hastega, I needed Haste. Y'shtola can use Magic Breakdown, so that meant Vanille was going to be my buffer with Shellga and Haste. I finally had a party:
You'll notice that pretty well every character is wearing a Mage robe of sorts, for Resistance. Most characters had 300 Resistance or more rather than the 250 I was using baseline for my calculations, which meant taking a further 39% less damage or so. Add to that Vanille and Y'shtola wearing Fire Resistance accessories, and my mitigation was through the roof.
You'll also notice that my two offensive casters weren't using Devotion or Impetuous Youth for their Record Materia. Those would reduce their Resistance, and frankly, survival was more important than DPS in this case, especially since I could capitalize on elemental weaknesses.
Combat with Rubicante himself still required a few S/L's. Interestingly, his first attack is always Blaze, which does 25% of the party's HP in damage, unmitigatable. This allows you a round to set up defenses, and solves to an extent the problems I had with other fights being RNG heavy and taking a blast to the face off the bat.
However, timing issues and figuring when to use abilities are really what caused me to have to reload a few times. Who to Haste first, in what order for maximum survivability. The timing of Steal Power got me a few times, too. Rubicante is fast. Even with Haste, if I hadn't started an action by the time his second attack got off, I usually waited until I could Steal power for his third to uncloak him. Also, Water spells have a faster cast time for some reason than other spells, so that timing threw me a couple times too.
Sentinel's Grimoire, my Wall, I had to hold off from using for the first 25% of the battle or so. I couldn't kill him fast enough to keep the buff for the entire battle, and he does less damage in the first 50% of his health than he does in the last 50% (Triple Firaga can go sit on a tack, thank you).
Woohoo! Nailed him! It was a hard fight, and when you think mobile games you don't necessarily think of the strategy required to beat an enemy of this difficulty. These Ultimate fights are really where FFRK shines in my eyes: when both the meta setup and the actual fight execution itself are a puzzle.
Despite having to go through 262,029 health to kill him, I had just enough ability uses to make it through. I had just run out of Steal Power, I was down to 1 heal left, no Soul Break power left in the tank for my two Medica users, both casters had maybe 3 or 4 casts left, and Balthier has 1 use of Watera Strike remaining when Rubicante went down. Talk about balanced on a knife's edge!
All in all, I've really been enjoying these fights. Well done, DeNA!