Monkeys take damage more or less identically to humans, except that they are immune to Fire Damage for some bizarre reason.
Monkeys have four sets of DNA like Humans, but only the SE DNA actually does anything. Monkey SE DNA is "2B6696D2B127E5A4".
In Monkey Mode, monkeys are viral and can transmit this infection to humans, which results in them turning into monkeys. The objective for the monkeys is to infect as many humans as possible, and escape on the shuttle. The humans must stop them from doing either of these.