Shadow lairs are currently dead content because of the prohibitive cost of entry. There needs to be a way to earn keys in game for completing a challenge. Doing a full arcade run without going down on elite difficulty is the most difficult achievement in the game and proves you can handle one. Reward this with a shadow key.

As a bonus, this will dramatically buff arcade and stop people from spamming vanaduke 24/7 while reinvigorating the rest of the game. Its the perfect fix and would be very simple to impliment.