The drop pool for 12-7 is very large. If you're specifically going for rare shields, you might have better luck farming the specific stage that is shield focused, which is stage 3. 

bad idea for rare shields :)

Why's that? Stage 3 doesn't drop rare shields on the boss fight?

Unfortunately you're  doing  it  correctly,  only  bosses  can  drop  the  rares  it's  just  rng. I've  skipped  this  everytime  but  I'd  probably  do  1-7 brutal  /  nightmare for  the  speeeeeed  and/or  lower  energy,  but  I'm  not  sure  if  the  rare  drop  %  is  lower  or  not.  

Because rare items only drop from the boss stage. Uncommon is the best you can do from stage 3s.

I think you should pass along to the devs to eliminate this quest.  Or ask one of the mods to post how this is helpful for account progression :)

Just to be clear - I mean farming 3-7, instead of 12-7, since 3-7 is shields

Someone  has,  but  I  can  double  tap  it.  

You say to be clear, but you're only confusing everyone more... :P Rare items only drop from boss stages, so this quest requires farming boss stages, regardless of which chapter or difficulty you're on, and there is no way to increase the odds of getting shields as opposed to any other rare item. 

I picked this quest thinking it'd be fairly straightforward, but not so much, indeed... 

Lol. My clanmate failed last week. Someone who doesn't chat took it this week. I am guessing they don't know what they are in for :)

Good luck. 

Does running normal make sense instead of brutal?

I did have like 2000 energy piled up from being pretty inactive lately... let's see how far we get. ;) I was even farming nightmare for a bit, changing things up and all, but although I did seem to get more rare drops there, the energy cost was too punishing so I dropped back to brutal. 

I would run Brutal just for that slightly better drop rate. Or Nightmare if I could do it efficiently time wise.

Perhaps a good idea would be to ask your developpers to try to fulfill the quest they asre creating by themselves by playing the game. In many instances I get the impression that none of them ever touches RAID. Best examples are 20 quests for 30 clan members (now solved but should have never appeared), the quests to do 20+ dungeons with rares from one faction, Bommel who in his current state cannot be beaten by 99.99% of the players and so on.

We're  just  players,  we  don't  work  for  plarium.  All  we  can  do  is  go  through  the  community  managers.

Like Harbby said, they are not our developers as we are just moderators. 

Also, I don't think any of us know what percentage of players will beat the new DT bosses. They look hard, yes. But they also aren't in the game yet for us to know.

I managed it - and of course, it just figures, in my last run of twenty auto fights I even got two rare shields, so ended up with 4 total. Wasn't keeping track of how much energy it took, but all in all probably something like 150 runs on brutal (and a few dozen on nightmare before that). 

for my own experience, to get the rare shield try bring less champion or bring 1 champion that can solo along 3 level 1 champion.. the rate maybe goes high

Before I lock up this unnecessary necro:

No, RNG does not get adjusted by doing this. Bringing less or more champions only affects how XP is split.