Beat it after too many tries, mainly because I didn't change units often.
Started with Horse Emblem and my Arena Team (Sharena, Azura, Tharja, Nino). Didn't work. Tried to use a bit of both, didn't work. Tried to use Cordelia and Michalis, didn't work. Tried to tank the top, didn't work.
So I changed and mixed a bit. I gave Azura Hone ATK 2, because Michalis lacked 2 damage to kill the Archer. In the end, this proved to be useless because Michalis never stood near her anyways. I also looked for a unit to tank the top, so a red one with high Res came to mind. The only one I had was Lyn. I have a 5* +1 Lyn, but she died to both attacks of the green cavallery and the red mage. With a +3 HP Seal she survived, but couldn't kill the red mage. So I gave her Escape Route 2.
So, in the end, it worked like this.
Lyn at the top, moved to the left, tanked both green cav and red mage. Michalis at the right, moved 2 tiles down. Nino at the bottom left, Azura at the bottom right. Nino moves right and drags Azura back. Azura dances Michalis and he moves onto the defense tile.
Nino kills the blue cavallery, Michalis moves to the right of Berkut and kills him with his special. Azura dances him and Michalis kills the Archer. Lyn uses Escape Route to escape to the bottom near Nino. Next turn, Lyn kills the green mage and I move my units so that Azura tanks the red mage on a defense tile and then kills him.
This was fun and I am never going to make fun of Escape Route ever again.