Danger Room or Battle Box is like normal Magic except for these rules:

• Each player starts with ten lands in reserve: two of each basic land. Each turn, a player may play one land from these ten lands. Lands are indestructible and can't be targeted. Players will never be mana flooded or mana screwed. There are no mana-producing cards in the cube. There can be cards that reduce the mana cost of other cards (e.g. Warden of Evos Isle (https://cubecobra.com/tool/card/ba0ec2d2-c004-4f6b-ba1c-29d81ad77fd1)). There are no cards that cost more than ten mana or more than two mana of the same color. There are cards with Domain abilities in the cube.

• Each player draws from a shared library that has no duplicate cards and balanced colors (i.e. the cube). The exception to this is if a card returns any cards to the library. Then the player has their own separate library and draws from that until they run out of cards. Then they draw from the cube again. There are no tutors in the cube. Cards that are returned to the bottom of the library will never be drawn again as the game ends if by some minuscule chance the cube runs out of cards.

• A starting hand is six cards. However, I've found it fun to have players draw ten cards and pick out a starting hand of six. The maximum hand size is nine.

https://strategy.channelfireball.com/all-strategy/mtg/channelmagic-articles/danger-room-renovation/