To get an S+ rank, you must meet certain requirements. Ranking is awarded based on five factors: difficulty, kills, collectibles found, number of deaths, and par time. It is also based on whether you are playing alone or with other players. Playing alone means you will have less stringent requirements than playing with others. Before starting a stage, look at the requirements for the Kills/Collectibles/Deaths/Time. There is a set amount you must achieve for the S rank. You must play the game on the Professional difficulty to get an S+ rank. Reaching each of the pars will get the S rank. To get the S+ rank, you must exceed all four settings. For examples, you will need to score more kills than listed, discover more collectibles than listed, not die at all, and finish the level earlier than the par time. Additionally, you must beat the par time by five minutes in certain circumstances.
Search the indicated locations to find all seven raccoon mascots:
After going down some steps, you will enter a large room with some sofas and server banks behind them. Check the back left corner, behind the servers, to find the mascot. You will find it before entering William Birkin's lab.
After passing through a room full of statues and using the main computer, you will go up to the second floor of the police station. From the balcony, continue forward while killing zombies. Straight from the double doors you just exited, you will find another set of closed double doors across the room. Open the doors to enter a new stairwell. Go up the stairs to find the mascot on the floor.
Mission: Lights Out
Inside the park, while collecting EMP devices from the UBCS Mercs, follow the right wall as you go through the area to reach a large sewer drain. The mascot is just to the right of the barred entrance.
Mission: Gone Rogue
After entering a large chamber full of green bio-tanks on rails, you will reach a central cylinder where the tanks are being shuffled through before the facility shuts down. Follow the left side around the central cylinder to find an opening inside. Go between the tanks to find the mascot at the dead-end.
Inside Chief Iron's office, down the hall with the stuffed tiger, you will be ordered to destroy more evidence. Once the evidence is destroyed, look on the cabinets to find the mascot in plain sight.
During the elevator ride, wait for your second stop. On this floor, search the backroom to find the mascot.
Mission: End Of The Line
Towards the end of the mission, you will see a group of zombies on one side of a fence. Wait for the zombies to break the fence down. There is a ladder nearby you must climb up, but do not climb it yet. Instead, circle right around the train to find the mascot at the end.