Vampire is an Arcade game mode. It is similar to Elimination mode (in terms of limited lives available), but has the additional factor of requiring the player to continue accumulating kills, lest their 'blood' will run out, causing a life to be lost as consequence.
In Timesplitters 2, this mode can be set to Deathmatch in the game settings (by changing lives to none and "Score Limit" can be set), while you still need kills to extend your life span. This however cannot be changed in Timesplitters Future Perfect.
Similar to Elimination mode, there is a pre-set amount of lives, with the aim being the last player standing with at least one life, or the most lives left within confines of a specified time limit. However, in Vampire mode, the player has a certain amount of 'blood', depicted by a red gauge in the upper area of the screen. Since it is constantly diminishing, the gauge must be replenished, or else a life will be lost. The bar can be kept at a sustainable level by killing the opponents.
The speed at which the gauge depletes is referred to as "bloodlust", which can be set to a low, medium, or high speed. When bloodlust is set to low, the blood goes down at a comparitively slow rate; when high the player needs to kill at a blistering pace in order to survive.
Games and Unlocks
Vampire mode is only available in TimeSplitters 2 and TimeSplitters Future Perfect. In TimeSplitters Future Perfect, Vampire is available from the start, whilst TimeSplitters 2 requires you to complete the Demolition Derby arcade challenge in order to unlock the said game mode.