Missions 1 to 4 Rewards
Complete mission 1 with the professional rating to unlock the "Quarry" map and with the slayer rating to unlock the "Female Vampire" character. To unlock the "Zombie Skeleton" character and the "Cemetery" map, get through mission 2 with the professional rating and the slayer rating, respectively. Complete mission 3 with a professional rating to unlock the "Zombie Demon" character. Complete it with a slayer rating to unlock Tara. Mission 4 nets you the "Bat Beast" with the professional rating and the "Zombie Devil" with the slayer rating.
Missions 5 to 8 Rewards
Complete mission 5 with the professional rating to unlock the "Materani" map. Complete mission 6 with the professional rating to unlock the "Psycho Patient" character and with the slayer rating to unlock Sid the Dummy. The professional rating unlocks the "S&M Slave" character and the slayer rating unlocks the "S&M Mistress" when finishing mission 7. Completing mission 8 with a professional rating will unlock Faith, and completing it with a slayer rating will unlock the "Initiative" map.
Missions 9 to 12 Rewards
Complete mission 9 with the professional rating to unlock the "Zombie Soldier" character and with the slayer rating to unlock Kakistos. Unlock the Abominator and the "Chainz" map by getting through mission 10 with the professional rating and slayer rating, respectively. Complete mission 11 with a professional rating to unlock the "Zombie Gorilla" character. Completing mission 12 with a professional rating will unlock Joss Wheadon.
Throw and Stake
The best way to kill vampires is to throw them, by pressing the "punch" and "kick" buttons simultaneously, and stake them while they are on the ground. No vampire in the game will be able to live after this combination. However, you cannot use this maneuver on boss enemies, as you will not be able to throw them.
Staking Vampires
If you knock a vampire down while fighting, stake him as quickly as possible. This will result in an instant kill and dramatically even the odds in your favor when dealing with vampire groups larger than two.
Blocking Enemies
If you are dealing with an enemy who is blocking all of your attacks, run away from him. This will make him chase you, at which point you can stop, turn around and attack as he runs at you.