Halloween Kurthnaga

Weapon: Lantern Breath+ (+Res)

Assist: Positional Assist

Special: Sol / Iceberg / Noontime

Passive A: Distant Counter 

Passive B: Dragon Wall / Dragon's Ire

Passive C: Pulse Smoke / Joint Drive Res / Joint Drive Atk / Atk Smoke

Sacred Seal: Quick Riposte / Atk/Res Solo

• Kurthnaga has great starting Resistance and a number of great Dragon-exclusive weapons and skills at his disposal. Due to the commonness of mages and ranged defenders in Aether Raids, a skill set that builds up Kurth's Resistance to near maximum levels while still maintaining a satisfying amount of power and physical durability is first on the table. 
• You don't need to look further than Kurthnaga's default Lantern Breath (Resistance refined to maximize magical bulk) as it provides many things Kurthnaga desires in a defensive weapon: his strength gets bolstered while the enemy's gets lowered (+5 Atk and -5 Atk, respectively), and on top of this, the enemy is inflicted with Special delay, making Special charging difficult if not outright impossible for them. The condition for these effects is merely either fighting in enemy phase or engaging an enemy with ​​HP ≥ 75%, both of which might as well be givens on a build that works exclusively by baiting attacks.
• Distant Counter is pretty much a given on any Aether Raids main tank to counterattack the most enemies possible. Plus, Kurth is taking full advantage of that dedicated Resistance investment versus the ever-prominent mage units inside and outside Aether Raids. 
• Also making nice leverage of all the dedicated Resistance investment is Dragon Wall, which provides damage reduction based on how high Kurth's Resistance is compared to the opponent's. Those who do outmatch his stats are few and far between, and with Mythic blessings like Eir's or Ashera's in effect, the number only gets smaller as Kurth zeroes out most magic attacks coming his way while greatly reducing incoming physical damage. Because it takes up the B-slot, however, Kurthnaga will be forced to take up Quick Riposte in the Sacred Seal to have some form of follow-up (required on this build to guarantee kills in most matchups).
  • Alternatively, you can run Dragon's Ire with Atk/Res Solo for a combination of better raw Attack and Resistance along with superior follow-up potential. In particular, Dragon's Ire basically guarantees that Kurth will double anything he's up against (especially Impact skill users) as long as he's not fighting something with Null Follow-Up and he keeps himself above 50% HP. Because Kurth's bulk is already as good as it is prior to further strengthening it, running a stat-booster like Atk/Res Solo to overwhelm the enemy as opposed to running Dragon Wall might also be preferred in many scenarios. This is also a good option your Kurthnaga doesn't quite reach enough Resistance to make Dragon Wall worth it (ideally, it should be around 50+ after Mythic Blessings and skill investment). 
• Without a way to quicken his Special charge (otherwise, you'd be using New Year Velouria or Summer Hilda/Marianne for instantly-charged Noontime on every attack), the build's best Specials boil down to the 3 CD Iceberg or Sol. Both should charge consistently every match factoring in a follow-up attack from Dragon's Ire or Quick Riposte, and your choice between them boils down to burst damage versus sustainability. 
• In the C slot, Pulse Smoke goes well with the Guard effect of Lantern Breath for the total prevention of future Special triggers from surrounding enemies. Lacking that, you can strengthen Kurthnaga's combat with either Joint Drive Res or Atk, or go with the cheap and good old Atk Smoke to further debilitate incoming damage. 

Weapon: Blackfire Breath+ (+Res) / Lantern Breath+ (+Res) / Pale Breath+ (+Res)

Assist: Positional Assist

Special: Glimmer / Noontime / Iceberg

Passive A: Distant Counter 

Passive B: Dragon's Ire / Dragon's Wrath / Lull Atk/Res

Passive C: Joint Drive Atk / Res Smoke / Atk/Res Menace

Sacred Seal: Steady Breath / Quick Riposte / Atk/Res Solo / Atk/Def Solo

• Our dear Goldoan Prince can also follow the steps of his festival-going father: simply eviscerate the utter living socks off of anyone who dares initiate into him. For this, more priority is given to Kurthnaga's Attack, increasing his damage per hit as far as possible to increase one-shots and general kills overall.
• Coincidentally, it's optimal to consider borrowing papa dearest's dragonstone: Blackfire Breath. Running it grants effectively the same stat swings as Kurth's Lantern Breath, but its bonus negation effect cancels out any Resistance bonuses the enemy might have and thus maximizes damage in all of Kurthnaga's outgoing matchups. At any rate, Lantern Breath is a fine budget option if you'd rather keep the Guard effect (helps Kurth avoid taking dire damage from short-charged Specials) or can offer Atk support from other allies to make up the difference.
  • Another option is borrowing his sister-in-law's Pale Breath+, which provides penalty negation in Attack and Defense and thus allows Kurthnaga to proceed without being significantly impeded by debuffs. Unlike Blackfire and Lantern Breath, though, it does not affect Kurthnaga's Resistance in any way; it boosts his Defense by +5 rather than lowering the enemy's Attack by -5, benefitting him purely in the physical department. 
• Distant Counter is yet again the non-negotiable A-slot option here as it's assumed you'll be running Kurthnaga at maximum solo efficiency and thus open him to a variety of matchups, especially ranged attackers in Aether Raids.
• Though Kurth's single-shot damage is prioritized, there will be times where you'll have to resort to a second hit to do an enemy in. Dragon's Ire is an exact and optimal solution for this, as it has a forgiving HP threshold of 50% (as opposed to Quick Riposte's 70%) as well as the ability to ignore skills that impede Kurth's incoming follow-up attack, such as Sturdy Impact. That said, if you're comfortable with running Quick Riposte instead as your source of follow-up or simply want to prioritize Kurth's damage per hit, you have a few B-slot alternatives. Dragon's Wrath, for instance, provides some resilience by reducing the opponent's first hit, and Kurth's Attack investment pays off as Dragon's Wrath also adds a considerable amount of true damage based on how high his Attack is over the enemy's Resistance. Lull Atk/Res is a tad more accessible than the previous options and should be used with Lantern Breath exclusively as it provides the same functionality as Blackfire Breath, but in a B slot. 
• The combination of the Steady Breath Sacred Seal and your choice of either Glimmer or Noontime as a 2 CD Special gives Kurth the ability to retaliate immediately with increased damage or healing on counterattack. If Kurth is getting his Special acceleration elsewhere (such as New Year Velouria's Renewed Fang or Summer Hilda/Marianne's Sunshade Staff) or simply isn't running a 2 CD special, you're good to choose from any other Seal that improves Kurth's stats or playstyle. Quick Riposte, for instance, gives Kurth a follow-up option in the absence of Dragon's Ire, and running either Atk/Res Solo or Atk/Def Solo greatly increases his power and defenses simply by spacing himself from other allies.
• Given the build's increased priority on damage, C-slots that help with the goal are taken here. Joint Drive Atk is the easiest way of doing so with respect to its immediate activation upon being near allies. Else, Res Smoke is more accessible than the other listed options and provides a widespread Resistance debuff on groups of enemies, and Atk/Res Menace's great effects but single-target behavior is best reserved for modes other than Aether Raids Offense. 

Weapon: Lantern Breath+ (+Def)

Assist: Positional Assist / Rally Assist

Special: Bonfire 

Passive A: HP +5 / HP/Atk 2 / HP/Res 2

Passive B: Even Pulse Tie / Axebreaker

Passive C: Infantry Pulse / Panic Ploy

Sacred Seal: Panic Ploy / HP/Def 2 / HP +5 / HP/Res 2 / Atk/Def Form / Atk/Def Solo

• Expensive things are expensive and waifu is laifu, so if you're pinching Orbs or simply have no desire to sugardad Kurthnaga anymore than required (he IS a dragon prince, after all), you can use him as the developers originally designed: a simple HP-stacking build with Ploy and Pulse-type skills as main options. In a nutshell, Kurthnaga's HP being as high as it is allows him to utilize his best intended fodder skill with low-cost ease: Even Pulse Tie. Or, if you just want another unit that handles most Axes efficiently and confidently, run Axebreaker instead in the B slot. 
• To maximize the effectiveness of Even Pulse Tie and any other HP-conditional skills run, running A-slot skill and Sacred Seals that directly add HP are ideal as well as inexpensive. HP/Atk 2, HP/Res 2, and HP +5, in particular, are common choices from the low-rarity pool. 
• Panic Ploy and Infantry Pulse piggyback off the existing HP investment with perks of their own; as long as Kurthnaga's HP is comparatively higher, he can either:
  • Use Panic Ploy to apply stat boost reversion to enemies in the same column as him.
  • Use Infantry Pulse to quickly precharge his infantry allies' Specials at the start of the match, allowing them to fire off powerful Special blows on tougher opponents without delay. 
  • If you don't mind losing out on some HP boosts in the Sacred Seal, Kurthnaga is easily able to run both in his C and Sacred Seal slots to maximize his support utility. 
• Beyond the mentioned skills and Lantern Breath (which is generally already a decent defensive weapon if Kurth is forced to scuffle, plus it can be refined to give a nice boost to Kurthnaga's HP), there's not much else to discuss except the Assist slot. 
  • In most cases, a positional assist is favorable; Reposition is great for most game modes while Smite improves his support utility in Aether Raids Offense. 
  • A Rally is also considerable if you'd like Kurthnaga to help out more actively with buffing bonuses, though this is only recommended if you can access a high-tier Rally and are confident otherwise in your endturn positioning. 
• Running an AOE Special without any cooldown support or Attack investment at all would be pretty unoptimal; thus, simply replacing Kurtnaga's default Growing Light with Bonfire should give him powerful emergency burst damage in the right situations.