13. Zombie Mansion - Timesplitters
One staple of the Timesplitters games was the zombie filled mansion level. These levels are often considered the most challenging but also one of the more fun. In the original Timesplitters, the level is set in a cursed mansion where a murderer's remains are causing zombies and mutants to run riot. It is widely considered to be the hardest mission in the original game, particularly on the higher difficulty. The mansion level also made an appearance in the challenges with the aptly named "Behead the Undead" and the aim of these challenges was to score points by knocking off the limbs of the undead, with heads being worth considerably more than arms and legs.
12. Floodgate - Halo 3
One of the best levels from Halo 3 reintroduce us to The Flood, the parasitic enemies that are hell bent on infecting and assimilating any sentient life they encounter. After Master Chief had destroyed the Covenant Anti-Aircraft Turret in the previous level, the UNSC attacks a Forerunner Dreadnought with Covenant Loyalists on board. The Dreadnaught survived and activated a portal leading to the Ark but to make matters worse, a Flood infected ship managed to get past Quarantine and crashed into Voi, Kenya. Almost instantaneously The Flood go about infecting and reanimating every dead body it could find. To get rid of this latest Flood threat, Master Chief and The Arbiter had to find the crashed ship and overload the engines, which would wipe out not only the Flood but the entire city.