Grand Hero Battle - Clarisse

Just put Xander on a defense tile and have Kagero/Azura clean up the what remains.

Throw xander on the defense tile 1st turn w/ camus close to exchange goad/ward. Camus can double blue mage ez, reinhardt can easily one hit the red infantry. Xander tanks everyone except blue mage. Much easier than inferno legion.

I used Robin to lure in Clarisse turn 1 by standing in the space to the right of the breakable wall and Ryoma lures in and kills the Green Tome (which is the only real scary thing for Robin). After that you kind of wall with Lucas while healing with Lyn when necessary.
Lyn can be replaced with any Rehabilitate user. And I'm sure Ephraim could do Lukas' job, I just don't have Ephraim

I beat Infernal with this team so it should work if you guys can figure it out ;)

RobinM going Triangle Adept 3+Sword Breaker 2 to basically nullify attacks from all foes save the green and blue mages. Using Bonfire as special. My Tharja doesn't have Death Blow, so I gave Robin Hone speed to buff Tharja so she can ORKO the green mage.
Tharja going Darting Blow 3 (Deathblow is better), Desperation 3 (useless, take your own B slot), New Moon as special (Luna is obviously better, Moonbow has same effect as New Moon).
Sakura going Physic and Imbue (any healer with distant heal and Imbue will do)
Olivia going Hone Attack 3
The Idea is to use RobinM as the tank and carefully take out the only remaining threats to him--the mages; especially the green one.
The fight can roughly be dissected in 4 phases:
P1: Take out the green mage: use the first 2 turns to place your units so: Robin is below the breakable obstacle, Tharja right below him, Olivia and Sakura to the left and right of Tharja. This way Robin baits the red swordsman, Clarisse and the thief, who do basically no damage to him.
On the 3rd turn, the green mage should be on the leftmost defensive tile, take her out using Tharja. The breakable obstacle is now broken by the thief. Move Robin to the resulting tile, attack the red swordsman. Sakura heals Robin, and Olivia moves Tharja out of danger area.
P2: Take out all enemies save the blue mage: This phase is relative simple. In this phase, you want Robin to stay in the same tile as before, so enemies are stopped at the choke point. First use Robin to take out Clarisse, who is now low from your counterattacks. The thief will die from your counterattack. Use Sakura+Olivia to double heal Robin (26 hp/turn). On turn 6, use Robin to take out the red infantry. Now you are left with only 2 enemies: the blue mage and the red cavalry.
Tharja, standing to the right of Robin, can take out the red Cavalry in 3 turns, after which New Moon is charged. Note that in this process Tharja will stand in the danger area, but she is safe. The AI will command the red cavalry to attack Robin, so the blue mage cannot move over to kill Tharja.
P3: Heal up: After Tharja kills the red cavalry, immediately move Robin to the red cavalry's previous tile. Continue healing Robin and Tharja, until they are full. DON'T make any move other than healing these two units until they are full.
Now, in a few turns you will be in the following situation: the blue mage occupies the uppermost defensive tile, Robin in the middle defensive tile. Tharja, Olivia and Sakura are placed so that Sakura can heal both Tharja and Robin in one turn. Continue like this until both Robin and Tharja are full.
P4: Kill the blue mage: My tharja doesn't have Deathblow, so the attack buff from Olivia is needed to do the job. After she is fully healed, move her to middle tile along the right edge of the map (right below the danger area). The blue mage will continue to hit Robin for 19hp/turn (38/turn if special is triggered). Keep an eye out for the special countdown and keep Robin alive in the process.
The final step is to bait the blue mage out of the defensive tile. Wait until the following conditions are met: Robin has 27+ hp, Sakura has imbue, and the blue mage's special countdown is 2+. In the following turn, move Olivia towards Tharja. Robin stays put. In the enemy phase, he takes a hit of 19 hp. In the next turn, move Olivia below Tharja so the latter gets attack buff. Sakura heals up Robin, so he has at least 26 hp. Then move Robin 1 tile upward. The Blue mage will be forced up 1 tile to attack Robin, which will not kill him. In the next turn, use Tharja and Robin to finish her off.

No unit merged, Ivs are not important (except -atk Rein).
Xander Reposition Bonfire Fury QR Hone Cavalry,
Camus Reposition Bonfire Fury QR Goad Cavalry,
Reinhardt Reposition Luna Atk+3 Goad Cavalry,
Hector standard vantage build.

Turn 1) Move Xander in Thief/Green Mage range, Thief will attack first and will be repositioned by Red Horse, Green mage suicides himself. Important: Move Rein under Xander to get hone buff for next turn.
Turn 2)Kill Clarisse with Rein(Camus buff+ Xander buff will be enough), reposition Rein out of atk range with Camus leaving Camus in Red horse range, move Xander in a safe tile and move Hector in blue mage range.
Turn 3) Kill Thief with Xander's Bonfire, put Hector to safety and move Camus in Red Infantry range.
Victory!