First of all: stop making new champs lvl 50. Instead, level up only food champs and make some of your actual lvl 50 champs lvl 60. You will get stucked with lvl 50 champs, like you actually see in Fireknight.

FK lvl 13 is force affinity. If you bring Galek, Kael, Scyl, Alure and Fellhound, 4 of 5 champs have weak affinity for that dungeon stage. They just don't survive the hits from the FK, especially when they are only lvl 50.

For FK 13, I recommend High Khatun (speed up your team, decrease speed debuff on her A1), Vogoth (triple hit A1 to deplete shield and his passive heal to survive, put him on team position no. 5), Armiger (to keep the shield down once it's depleted, this effect needs 100% crit rate and accuracy), Dagger (decrease def, especially to speed up stage 1 and 2 of the fight, and she has some minor tm effect on her double hit A1), Alure (just to good in FK, even with weak affinity, use hp% chest to make her survive).

Stragey is not to let the FK gain turns and use Fellhounds reflect to deplete the shield, but to deplete it with Vogoth's and Dagger's multi hits and keep it down with turnmeter reduction once you got it down. Your champs need to be fast to achieve that.

Skadi thank you so much for this help. As far as which champs are food this is where I get spun around as there are so many youtube vids stating the use for different things for different champs. Thank you again for taking the time to help.  

None of the allready levelled and ascended champs are food! Don't waste the effort you put in them.

Buy a random uncommen at the market or open some green shards and start levelling up uncommen champs in campaign. One Champ as "farmer" (Kael with lvl 60 should work well) and 3 champs that are only leveled up to serve as food for others. Campaigne stage 12-3 brutal is quite easy to do, gives high exp and silver (sell the shields you get as loot). 

The food champs get no ascension and no equip, they get sacrificed anyway.

5 rank 5 champs needed to bring one champ to rank 6.

4 rank 4 champs needed to bring one champ to rank 5 (20 for 5 champs).

3 rank 3 champs needed to bring one champ to rank 4 (60 for 20 champs).

2 rank 2 champs needed to bring one champ to rank 3 (120 for 60). 

So yes, it's a lot of repetitive grinding, but unless you want to spent all your money on chickens, it's the way to get champs to lvl 60. 

Thank you again for this. Got a lot of grinding to do.