You need turnmeterreduce vs. Fireknight. First bring the shield down with multihitters like Vogoth, and when it's down, keep it down with champs that reduce his turnmeter (has no effect as long as the shield is up). 

Scyl with her A1, Armiger (uncommen champ, easy to get) and Soulbond Bowyer can do that. 

Team: High Khatun (lead), Vogoth, Armiger, Soulbond, Scyl.

The next stage 19 will be hard, as most suggested champs are spirit champs and will have weak affinity at 19, but you just have to do stage 19 only once.

Did you get Scyl from a shard? Your champion roster is quite small for 180 days of playing.

Agreed you need turn reduction, however there aren't enough multi hitters to get the shield down, if it does go down you need heal reduction if you can't keep it down - and he also has to get through two waves, it's unlikely with that roster he could get a team through the waves, that can then take the shield down, put a heal reduction on or keep the turn meter down long enough to defeat the boss

i  got  her  from  Blue  Shard  and am  3  mission  to  get  Arbiter  am  on  Stage  22  on  Spider  and  Doing  100  milion  to  Nightmer  CB  is  not  problem  i  have  900  gems  i  can  buy  keys  only  Fire  Night  is  problem  

Zavia, Scyl, Ninja, High Khatun and I guess Soulbond Bowyer, should get you through the waves and through the shield okay but you might not have enough TM reduction there, nor heal reduction. Adding Armiger instead of SB might help with that, but even then, not sure. Luria for Ninja maybe, but her A1 is so RNG that you can't rely on her for heal reduction...