As usual, Global ratings are my own opinions relative to other character or TMs available at the time this is written, with Japanese ratings coming from altema.jp. Japanese TM ratings are on a scale from: Unranked, B, A, S, SS, to SSS.

I'm moving the format of these back a bit to the way I used to where I'm only going to highlight the 'useful' skills characters bring to the table rather than listing their entire skill and passive lists. Multiple single target abilities? I'll only mention the best (unless the secondary ones have uses -- even niche use.) Physical character that has elemental magic spells for no good reason? I won't be bringing them up. Generic damage limit break? You get the idea. If you wish to see their full skill list please follow the links.

ARC:

Rarity: 3* to 5*

Global Party Rating: 8/10

Arc is a Black Mage with decent MAG (107 MAG 20%) who has access to all three core elements (Firaga, Blizzaga, Thundaga), Osmose, Death (OHKO 30% Chance), and DUAL BLACK MAGIC.

He doesn't have MAG as high as Kefka or Exdeath, and doesn't have huge combo finisher like Kefka's Hyperdrive, but in almost all situations Dual Black Magic will be enough to make Arc the strongest mage on Global (but 6* Exdeath is coming "soon")

Interestingly for a Black Mage, his Limit Burst is a group heal and MAG buff (AoE ~400 HP Heal w/ 9x Mod split over 3 Turns & AoE 3 Turn 40% MAG -> AoE ~400 HP Heal w/ 9.95x Mod split over 3 Turns & AoE 3 Turn 59% MAG depending on rank) which gives him some extra utility.

Japanese Character Rating (altema.jp): 80/100

Global Trust Mastery Rating: Omnirod - 8/10

Weapon - Rod - 20 ATK / 91 MAG

This is the strongest Rod on Global, and still the second strongest in Japan (only being beaten by the Emperor's Rod, but do note that he's a 5 star base.)

Japanese TM Rating (altema.jp): S Rank

Why would you want Arc?: He's a full featured Black Mage (Dual Black Magic!) with a great TM and he's only a 3 star base.

Is he FUTURE-PROOF?: Arc does not have 6* access in Japan.

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INGUS:

Rarity: 3* to 5*

Global Party Rating: 7/10 (If you already have Full Break, 5/10)

Ingus takes the role of a Red Mage and with that he has a variety of skills including White Magic (Curaga, Cura, Esuna), Black Magic (Fira, Aerora), Status Effects (Sleep, Blind, Silence) and FULL BREAK.

Unfortunately he has low SPR for his heals (89 SPR), low MAG for his spells (90 MAG 20%), and okay ATK which will only apply to Full Break (102 20%)

Ingus also has Convert which fully recovers his MP but reduces his HP to 1. This means as long as you have someone that can afford to heal him, he can keep casting forever.

Finally, his Limit Burst is an AOE Fire Magic attack which lowers SPR more than Full Break (and as strongly as Delita at 5 star, and more strongly if you rank up his limit burst) which increases your party's magic damage. (250% AoE 6 Hit Fire Magic Attack & AoE 3 Turn 40% SPR Debuff -> 345% AoE 6 Hit Fire Magic Attack & AoE 3 Turn 59% SPR Debuff depending on rank.)

Japanese Character Rating (altema.jp): 60/100

Global Trust Mastery Rating: Letters and Arms - 5/10

Ability - 50% MAG when equipped with a sword

This is really awkward to use and is competing with Shantotto's TM (30% MAG) for the slot. The best sword with MAG on it in Global or Japan is Enhancer with a not so impressive 23 MAG. Some other mages can use swords (such as Exdeath) but many cannot thus this is useless for them. Assuming you are using a mage who can equip a sword and you can give them Enhancer the extra 20% MAG over Shantotto's TM would need to total more than the MAG lost by not equiping a better rod. For Example, if the best rod you have is the Lilith Rod (60 MAG) you would only be better off using Enhancer and this TM if the mage you are equipping it on has higher than 185 MAG base (and so far, none of them do.) If you have the Wizard Rod (72 MAG) they would need a laughable 245 base MAG.

EDIT It seems this is stacking on Global. This makes it harder to rate as it's only particularly strong if you stack multiples -- if you are willing to stack 3 on a character it's 9/10.

This can have a niche use on 6 star Bartz with his 540% Hybrid attack (thanks /u/dimitryvegas)

Japanese TM Rating (altema.jp): A Rank

Why would you want Ingus?: If you don't already have a unit with Full Break, here's another one that's a base 3 star. Unless you need him for the extra healing he brings from Cura / Curaga, you're likely better off with any other Full Break unit.

Is he FUTURE-PROOF?: Ingus does not currently have a 6* upgrade in Japan.

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REFIA:

Rarity: 4* to 6*

Global Party Rating: 10/10

Refia, at release, has no competition for the best healer on Global (Will we finally see the end of threads trying to make White Witch Fina work? Hopefully!) Refia has high SPR (150 SPR 30%) and MP (181 MP 20%) allowing her to take full advantage of her variety of White Magic including Cura, Curaga, Curaja, Esuna, Dispel, Stona, and the amazing Arise (Single Target 100% HP Rez.) She can cure all status effects in the game with the exception of Disease, but that can be covered by Cleanse from Siren, Fran's TM (I'm not recommending you grind this out!), or by using items such as Remedy or Vaccine.

Refia has an improved version of Cheer called Embolden which is a 5 Turn 45% AOE ATK/DEF buff (compared to Cheer's 3 Turn 40% ATK/DEF)

She also has a passive called Talisman of Kazus which is a 100% Silence/Paralyze/Confuse/Petrify Resist.

Finally, her Limit Burst is an AOE Cure all status effects and DEF buff (AoE Cure All Ailments & AoE 3 Turn 40% DEF -> AoE Cure All Ailments & AoE 3 Turn 64% DEF depending on rank.)

Japanese Character Rating (altema.jp): 93/100

Global Trust Mastery Rating: Mentality - 6/10

Ability - 20% MP / 30% SPR

Slap this on your healer and they'll have a bigger MP pool to heal with, bigger heals, and take less magic damage -- the only problem is that the impact from those things is just not as strong as offensive TMs you likely have access to farming instead.

Japanese TM Rating (altema.jp): A Rank

Why would you want Refia?: Refia has a very complete kit and can be your main healer for months AND has an absolutely adorable victory animation.

Is she FUTURE-PROOF?: Refia is 6 star capable. Refia has received Ability Enhancements in Japan which include lower the mana cost on Arise from 20 MP down to 5 MP, Talisman of Kazus from 100% Silence/Paralyze/Confuse/Petrify Resist up to 100% Silence/Paralyze/Confuse/Petrify Resist & Recover 5 MP per 5 steps & Recover 5% MP per Turn, and finally Embolden from AoE 5 Turn 45% ATK/DEF to AoE 5 Turn 45% ATK/DEF & AoE ~1150 HP Heal w/ 8x Mod split over 5 Turns

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LUNETH:

Rarity: 5* to 6*

Global Party Rating: 10/10

Luneth is the first character to really to toe to toe with Lightning, and like Lightning, has innate Dual Wield. They have fairly similar ATK (Luneth at 146 30% 20% with a sword vs Lightning's 145 30% ATK) and Luneth has a higher single target attack in Spearhead (250% ST 1 Hit Physical Attack Ignore 25% DEF which can be normalized to a 333%) vs Lightning's Crushing Blow (270% ST 4 Hit Physical Attack & ST 3 Turn -20% Thunder Resist.) Both characters also have a 180% AOE Physical Attack and identical Limit Bursts (290% ST 1 Hit Physical Attack & ST 3 Turn 30% DEF Debuff -> 410% ST 1 Hit Physical Attack & ST 3 Turn 54% DEF Debuff depending on rank.) Both Luneth and Lightning also have a 30% chance to counter physical attacks and auto-refresh (recover 5% MP per turn -- like most 5 star base characters.)

What Luneth lacks over Lightning is the variety of Elemental attacks Lightning brings to the table (Luneth has none) and Lightning's 30% Chance to dodge physical attacks (but fairly balanced against Luneth's 100% Blind/Paralyze/Confuse/Petrify Resist.)

Luneth does have a slightly smaller set of weapons than Lightning -- both can use Dagger, Sword, Greatsword and Katana, but Lightning can also use Bows, Spears, and Guns.

Japanese Character Rating (altema.jp): 90/100

Global Trust Mastery Rating: Celestial Globes - 8/10

Accessory - 30 ATK / 30 DEF / 30 MAG / 30 SPR

This is a strong and flexible accessory but on a 6 star character this is effectively ~15 more ATK (or MAG) and some extra defensive stats over a Hero's Ring. If you put this on a physical attacker with Doublehand it will be more impressive. It's good but just not as much of a game changer as it might appear.

Japanese TM Rating (altema.jp): S Rank

Why would you want Luneth?: He's obviously a very strong physical attacker, and if you haven't already finished off several Zidane TMs (or even HAVE several Zidanes) that innate Dual Wield will be huge.

Is he FUTURE-PROOF?: Luneth is released with 6 star, but has not yet received Ability Enhancements in Japan which makes him lag behind some newer 6 star characters in Japan.

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Should You Pull?: Absolutely yes -- when the worst unit on a banner has Full Break, you know it's a great banner. This will likely be the best banner we see for awhile. Ingus has Full Break (but the worst Full Breaker on Global), Arc is a great mage (but his days are numbered once Exdeath comes out), Refia is a top tier healer which stays that way for the foreseeable future, and Luneth is right up there with Lightning.

BONUS: OFF-BANNER 6 STAR UPGRADES

CLOUD OF DARKNESS

Rarity: 3* to 6*

Global Party Rating: 9/10

CoD gets a 6 star upgrade and with it gains an extra 20% HP passive, 30% ATK Passive (bringing her ATK to 149 ATK 50%,) Man-Eater (75% Physical OR Magic damage vs Humans), Veil of Omnipotence (AOE 3 Turn 30% All Elements), Aura Ball (AOE 3 Turn -30% ATK Debuff and 40% chance to Silence), Reunion (AOE Cure Poison/Blind/Sleep/Silence/Paralyze/Confuse) and Invitation to the Void (210% single target 1 hit dark physical attack and ignore 25% DEF which normalizes to 280%)

Most importantly, CoD now has 4 Materia Slots to work with instead of the 0 she had before!

Japanese Character Rating (altema.jp): 89/100

How is her upgrade?: CoD now has incredible ATK, still has Barrage, and brings a little more utility than she had before. CoD at 5* had two main weaknesses: the lack of ability slots (now fixed) and limited weapon selection (which is still in effect.) If you have CoD and have a decent weapon for her you'll love 6 star CoD -- especially when you're fighting humans!