May have been suggested before, but how about a survival mode, in which a series of fights have to be beaten without troops returning to life inbetween and without healing / restoring stats inbetween.
It could probably simply latch onto the existing Challenges - the player playing through a kingdom’s challenges in order but as one big fight with 7 stages.
To make things more interesting (and to prevent some Legendary builds from simply steamrolling everything), players could be provided with a pool of troops to mix and match into their Challenge team - similar to Arena but with just a tad more control - perhaps a choice from commons, rares, ultra-rares but having all options visible while choosing.
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