Although I dislike using Duchess for this, she seems to be your only 2-turn duration block debuffs champ. So, use this tune:

https://deadwoodjedi.com/speed-tunes/single-43-block-debuffs/

Specifically,

https://deadwoodjedi.info/cb/55f338ec8f3b8d14a59e838a4cb319faf2481e4c

Replace Sepulcher with Duchess

Replace Frozen Banshee with Venomage

Replace Bulwark with Geomancer

That should easily let you 1-key NM, probably even get you into a comfortable 2-key UNM.

You can buy extra keys for 100 gems in the shop. If you can do 10 million per fight and use 3 keys each day anyway, 400 gems, buying 4 additional keys will do the mission.

There's also the server issue/maintenance/update packs they give out , those contain 1 CB key that will last 2 days in your mailbox. 

Also there's some tricks to make the CB key refresh happen on the time you want ... let it fill up to 2 , then use one when you want (for me 2pm/8pm/2am/8pm is where i set it so i can easely use my 4 keys daily , then i just bought the rest for when i was on those missions , like skadi mentionned above !

Hi, thanks for the replies, have been swopping my teams about. LoL never thought about that, still nowhere near the 75m but closer, maybe I will hit on the team that will do it, maybe I will have to wait for a couple of extra keys to drop, either way TBH doesn't really matter as completed the high elves faction wars so not a mad rush to get Arbitor as she won't make a major difference to my teams so will just mark time till I hit the required score.

I think you should change your priorities. IMO, getting top UNM and NM chests should be your #1 objective. It's by far the biggest source of books and shards of all types, but especially for epic/lego books.

This is when the game changes and begins to open up. Focusing UNM/NM as quickly as possible is a great strategy,

Hi, yes a few extra leg books would be nice. But I have completed the dungeons apart from sand devils which I have little interest in. I have completed all doom tower except 120 on dark fey, hoping to do it this time round as I have worked out a viable team. I have completed all campaign battles. Basically my challenge is to complete faction wars, As you can see I haven't got zillions of troops yet. Sadly time is against me when playing and the demon lord always seems to take ages and ages so has never really rocked my boat. I do it for daily tasks and now for the Arbitor quest, much the same as arena and tag arena. But thanks for the advice it is welcome.

I can almost guarantee you that the reason you are turned off by CB, is because you're used to either needing to run it on manual to get "good" results, or running it on auto and getting random and unpredictable results.

The link I pasted above gives you the speed tune ranges for your champs, and the auto-AI settings. Once you have those locked in, CB becomes a matter of just hitting "start", potentially playing the first couple of turns, and then hitting auto. At that point you just start raking in the rewards.

As for Doom Tower - my guess is that you've only done the normal mode. You really want to also be doing hard mode, since, again, the rewards really start ramping up.