The player begins the mission at the beginning part of the story mode level "Takedown" that's not too big. The player's objective is to attack and defend against the numerous militia in the village and also keep civilian casualties to a minimum, so they must watch their fire. The amount of enemies they face depends on the level's difficulty: on Regular, they need to kill 30 enemies and can only kill up to 6 civilians. On Hardened, they will have to kill 40 hostiles (including dogs) but can only kill up to 4 civilians. In Veteran, they'll have to kill 50 enemies (again including dogs) but the player can only kill 3 civilians. As always, if a player is damaged too much in co-op, they will be put into Last Stand.
There are several care packages containing ammo distributed throughout the level, so if the player runs low on ammo and doesn't want to scavenge for a new gun, these packages can be useful.
There is no set limit of enemies within O Cristo Redentor, rather the enemy constantly respawns and they will keep doing so until the player has reached the score limit, in the same manner as "Body Count."
O Cristo Redentor is one of two levels in the entire Call of Duty series that allow the player to kill more than one civilian without failing the mission (The other being "No Russian"). However, "No Russian" has no limit to the civilians the player can kill, while "O Cristo Redentor" has a cap on the amount the player can kill, depending on the difficulty selected.
If the player uses noclip console command and goes out of O Cristo Redentor and heads to the streets, they will see Ghost, Meat and Royce running toward the alley the player chases Rojas' assistant through on the campaign level "Takedown". They will also notice that there are also civilians running around the street and cars on fire. Plus in the alley, Ghost and his team will run through the forklift that prevents the player from returning to the streets and then stop. If the player kills Ghost, or any of the civilians outside the map, they will not be penalized.
At the end of O Cristo Redentor, there is an ammo crate, where on the campaign the player would go to catch Rojas. There is a house near this ammo crate. When the player enters the house from that side, throw a grenade into the door to the other side of the house. It'll get stuck in the door midair and blow up.
For every 10 human enemies the player kills, two or three dogs will spawn and chase the player including after killing the last enemy when the player will be able to hear the barking of another set of dogs as the level ends.