Dark Tower is one of the fight game modes in the Dungeon of Trials and becomes available for the players at League 20.
You can find the Dungeon of Trials on the main screen of the game:
Dark Tower is included in the rotation of the Pit - Dark Tower modes. Each mode lasts one week (7 days). After this period, a new mode opens and access to the previous one disappears. The modes change every Monday at 10:00 UTC.
In the upper left corner of this mode's window, the player can see a timer showing the time remaining until the end of the Dark Tower:
In this mode, players will face 16 different opponents, which get harder to defeat with every win. The match starts when the Fight button is clicked.
As soon as the battle begins, the player will be given a choice of 4 cards of a certain rarity from their collection (legendary, epic, or rare heroes). After the player selects a card, the rest 3 cards will disappear, and 4 another cards will be available for the next turn.
If the match is won, the player receives rewards for the floor. In case the match is lost, the player loses one attempt (skull). 1 attempt is restored in 12 hours.
If the player wants to continue playing, but he has no more attempts, he can buy it for gems. This option appears when there are no any skull:
From the Dark Tower players can receive Copper Coins, Soul Dust, rare, epic and legendary heroes. If there is an active Event, players will also receive Event Runes. The higher floor – the better rewards!
The Copper Coins can be spent in the Black Market, which is a special shop of the Dungeon of Trials, where players can get more hero's cards: