The Hunter

From wikipedia

An agile Infected who can climb walls and jump over rooftops, similar to 28 Days Later Infected and Half-Life 2's Fast Zombie. If the Hunter crouches for a certain period of time, a meter will fill and it can use its most powerful attack (this was chosen instead of it becoming invisible once backed up to a wall or similar piece of cover, turning invisible, and then pouncing). It can then pounce on a survivor, pinning them down on the floor and slashing at them with its claws, rendering the victim powerless unless The Hunter is killed by a team-mate or knocked off its victim. It is extremely weak, and can only sustain minor gunfire before dying. The Hunter can also retreat, and slowly heal itself.