Instead of a room of 4 or 5 soldiers like most Zombie Mode maps, this map is extended up to 8 soldiers, minimum of 3 soldiers required to start the match as usual. Upon the match, soldiers have infinite reserve ammo equipped. Uniquely, there are only two difficulty levels for soldiers to choose from. Even though there two different difficulty levels, the Reward Crates are the same, the only difference is the bonus reward:
Hard: Default setting like any Zombie Mode maps. The highest bonus reward rank is S+.
Nightmare: Five lives by default (Two in servers with 8 default lives), supporting items such as HypoMed-S, HypoMed-L, Intrusion Coins and Revive Token are disabled. The highest bonus reward rank is SS.
Trivia
Despite HypoMeds not allowed in Nightmare difficulty, players can still select them by pressing 5 / 6.
The timer stops at 15:00 before entering the third stage. This can be used to recover teammates and collect weapons. When players are ready, go to the main boss room to start the timer again.
This map's reward boxes in CFBR are called "Ruínas GF" which probably stands for IceFire Ruin (Gelo [Ice] & Fogo [Fire]), which stands for the Chinese version's name of the map.
Due to the limited 8 default-lives per day in CF Vietnam and Brazil, players will always start with 2 lives in this map regardless of chosen difficulty. This makes playing Nightmare a lot harder because of the lowered life available and once 8 lives have been spent players wouldn't be allowed to die at all in Nightmare difficulty.
As of Sep 2019 update, CFVN has partially fixed this problem by restoring the 5 lives on Nightmare difficulty. Now players will always use up to 2 default lives in NM even if they died 5 times, and when all 8 lives have been used up, players will start with 3 lives for the rest of the day. This means players who own M4A1-S Jewelry can partially play full-time as they could have 4 lives once 8 lives have been used, just 1 short of the default 5.