Roll Call is a daily reward system that's available to Guild members only.  As more members check in, the better the daily rewards.  You can earn Gems, Ritual Elixir, and Gold!

There are five tiers of rewards.  You need 1 check-in for the first tier, 7 for the second, 13 for the third, 19 for the fourth, and 25 check-ins for the fifth tier.

If you're in a Guild, all you need to do is visit your Guild screen and press the green, "Check-in" button on the right.  Remind your Guild members to check-in and get the best rewards!