Not with an unkillable team, no. Teams that go past 50 turns are typically ones with big defensive capabilities (shield, strengthen, DEF up, etc...)

My old CB team was Lydia, Aniri, Brogni, Martyr, and Dark Kael. I was *just* about at 1-key UNM with it. Usually lasted to around turn 65.

I see. Is there some aspect of an unkillable team that the game recognizes and knows to end at turn 50?

Pretty much. At turn 50 CB begins to ignore unkillable and block damage

CB has a passive called "Gathering Fury", which stacks counters every CB turn:

Gathering Fury [Passive] Starting from the 10th turn, the damage inflicted by all Skills increases each Turn. Damage increases by the same percentage each Turn, and accumulates over multiple Turns. Starting from the 20th Turn, damage is increased by a greater amount. Starting from the 50th Turn, all attacks will ignore any Block Damage and Unkillable buffs on each target, and applies Block Revive on champions that the Clan Boss killed. 

I do nightmare at the moment and I use shields and def up ect and it's really the only way to go beyond 50 block damage is for heavy hitters to do damage fast as possible without dying 

@djs078 

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So this would be the full example of what one of the killable comps and what it might want in terms of survival/taking maximum turns (my team from a run today): 

Brago: defense up/attack down

Brogni: shields, extension, block debuffs

Aniri: passive healing, buff extension

Lydia: strengthen, speed buff

Toragi: ally protection (this is the big one, imo), attack down

Ally protection on a champion with Stalwart/proper defensive stats is really going to be what lets these types of comps go far beyond 50 turns. 

Also, that is my run from today. Thanks @harleQuinn for encouraging me to switch to this killer comp, and for building Brogni, who is the linchpin for these comps. 

32 minutes....I'm pissed enough my runs take 23.

My Unkillable team caps at Turn 50 yes

But my Damage team will go turn 54 -56 easy on Brutal and  lower  lvls cb 

...now  if only I had a damage team that could do that on NM and UNM (meaning my damage team die before turn 50 currently )

Happy to help!

It's a fun comp for sure.

My heli team can go 52 with only heli surviving past 50. The ones that go 60 are based on actually getting those champs.