Team Comp: Buffer, Red Mage, Green Mage, Dancer
Tired of trying to kite the reinforcements to survive? Well then just forget about them! In this guide, you will learn how to clear Legion's grand hero battle on inferno difficulty, in a single turn! We have broken it down with a video, step by step with screenshots and full character builds you can paste into the KageroChart combat simulator.
Further down we also have an alternative strategy for those that don't have the resources to pull off the first strategy.
Legion GHB One Turn Clear (OTC) Video - Infernal
STEP ONE - Allied Red Mage Kills Right Legion
Allied red mage is buffed passively at the start of battle by the buffer and the dancer. Red mage kills the legion on the right.
STEP TWO - Dance Allied Red Mage and Kill Left Legion
Dancer dances allied red mage to give them a second turn.
STEP THREE - Allied Red Mage Kills Left Legion
Red mage moves into position and kills the legion on the left.
STEP FOUR - Buffer Repositions Green Mage / Hector
The buffer repositions the green mage / Hector.
STEP FIVE - Green Mage / Hector Swaps Dancer
Green mage / Hector swaps the dancer out of harm's way.
FINISH - Defensive Victory
The green mage / Hector baits and kills the enemy blue cavalry mage. Allied red mage tanks and kills the enemy archer and enemy red mage. Enjoy the 2k feathers.
Tharja [+SPD/-RES] 39 HP / 45 ATK / 37 SPD / 23 DEF / 17 RES Weapon: Rauðrblade+ Special: Sol Passive A: Darting Blow 3 Passive B: R Tomebreaker 3 Sacred Seal: Quick Pulse
Need to be able to ORKO both Legions (first the right and then the left) with dance assist. The archer attacks first, so you will need to be able to tank the archer.
These is only one real option since the red mage needs to be fast enough to double all units, while tanky enough to survive the archer's attack and remain above 50% to proc R Tomebreaker 3 (though having enough hp to survive the red mage should be more than 50%).
With Tharja, you must use Sol with the Quick Pulse seal instead of Noontime to improve survivability.
Tharja must have a +SPD boon since it revolves around being able to double the Legions without the help of Axebreaker and should not have a -DEF bane due to the threat of the Brave Bow+ archer nor can she have a -ATK bane due to Aegis on the second Legion.
If Tharja has a -ATK bane then you will have to adapt the strategy to also include Rally and Drive Atk 2 when it is eventually released (thanks to /u/WeeboSupremo for noting that -ATK bane falls short), otherwise the second Legion will survive. Another more contemporary alternative would be to use Rally and Drive Def 2 instead (replacing Quick Pulse seal with Atk +1 seal and Sol with Noontime). Similarly, just adding Drive Def 2 can make up for a -DEF bane. The execution of such compositions is left as an exercise to the reader.
Cecilia [+SPD/-ATK] 36 HP / 42 ATK / 33 SPD / 22 DEF / 29 RES Weapon: Gronnraven Assist: Swap Passive A: Speed +3 Special Seal: Speed +1
Nino [+DEF/-ATK] 33 HP / 43 ATK / 36 SPD / 22 DEF / 26 RES Weapon: Gronnblade+ Assist: Swap
Robin (F) [Neutral] -- 3 Star(s) 36 HP / 35 ATK / 25 SPD / 25 DEF / 19 RES Weapon: Gronnwolf Special: Swap Passive A: Attack +3 Passive B: B Tomebreaker 2 Special Seal: Attack +1
Swaps the dancer out of harms way and baits the blue cavalry mage. Gronnblade+ relies on the buffs in order to secure the kill. Robin (F) is a low-econ GHB unit that can do that job as a 3-star unit.
The Gronnblade+ options require buffs to kill due to the high RES of the blue cavalry mage.
Eirika [Neutral] -- Lvl. 1+0 18 HP / 23 ATK / 9 SPD / 7 DEF / 6 RES Weapon: Sieglinde Assist: Reposition Passive C: Hone Spd 3 Sacred Seal: Fortify Res 1
Ephraim [Neutral] -- Lvl. 1+0 19 HP / 25 ATK / 6 SPD / 8 DEF / 5 RES Weapon: Siegmund Assist: Reposition Passive C: Hone Spd 3 Sacred Seal: Fortify Res 1
To buff the blade mage(s). Reposition is to move the swapper into position.
Eirika and Ephraim aren't really needed though, as you can use any unit with Rally and Hone to replicate their effect so long as your green unit isn't armored.
Levels don't matter since the buffer will never participate in direct combat.
Azura [Neutral] -- Lvl. 1+0 17 HP / 5 ATK / 7 SPD / 4 DEF / 6 RES Assist: Sing Passive C: Fortify Def 3
Ninian [Neutral] -- Lvl. 1+0 16 HP / 5 ATK / 7 SPD / 6 DEF / 5 RES Assist: Dance Passive C: Fortify Def 3
Olivia [Neutral] -- Lvl. 1+0 17 HP / 6 ATK / 7 SPD / 5 DEF / 4 RES Assist: Dance Passive C: Fortify Def 3
Allows the red mage to kill both Legions.
Levels don't matter since the dancer will never participate in direct combat.
Unfortunately it seems I forgot to account for the dancer being in the line of fire in these calculations, so that would require the dancer to have at least Distant Counter to be able to kill the Blue Mage Cavalier. Big thanks to Heiliger Fakewooder for pointing this out.
Tharja [Neutral] 39 HP / 45 ATK / 35 SPD / 26 DEF / 20 RES Weapon: Rauðrblade+ Special: Noontime Passive A: Defense +3 Passive B: Axebreaker 1 Passive C: Spur Atk 3 Sacred Seal: Speed +1
To make up for the lack of a +SPD boon, Tharja relies on the ally green unit to provide a speed buff via Spur Spd 3. In fact, Tharja can be pretty much any neutral SPD nature.
Green Ranged Units
Hector [+ATK/-RES] 52 HP / 55 ATK / 24 SPD / 37 DEF / 16 RES Weapon: Armads Assist: Pivot Passive A: Distant Counter Passive C: Spur Spd 3 Sacred Seal: Spur Def 1
Cecilia [+SPD/-HP] 33 HP / 43 ATK / 29 SPD / 22 DEF / 29 RES Weapon: Gronnraven+ Assist: Pivot Passive A: Triangle Adept 3 Passive B: B Tomebreaker 3 Passive C: Spur Spd 3 Special Seal: Spur Def 1
Hector must have a +ATK boon. Cecilia must have a +SPD boon and cannot have a -ATK bane.
There are many other heroes with a similar build to Cecilia's abusing the synergy between Gronnraven+ and Triangle Adept 3, but they would have to inherit Gronnraven+ from Cecilia anyways.