My idea is this is to have some thing similar to the mimic card as a dragon troop. Call it Something like “Dragon’s hoard” (imagine a sleeping dragon on it’s hoard) The card would be a 50/50 shot of getting something amazing or doing some serious damage to your own team. It’s spell could be called something like “Stealing the hoard” or “taking a gamble” or “calculated risks” or “don’t wake the dragon”
50% chance to win 3-5 prizes of rare (ultra rare?) or better prizes (troops, trait stones, gold or keys) and would act in a similar way a chests would.
50% chance to attack your own team, doing significant true damage to an ally.
“dragon’s hoard” could have high attack damage but very poor armor or life stats. The stats might need some tweaking to balance it out) The point of the card would be to ‘gamble’ with it and see if you win or lose. Not very useful for GW or PVP but might make an interesting way to grind for more resources.