Vamp makes you perform multiple skill tests in one single action, which can be used in some fun combos.
Fun combo 1 : Preston Fairmont can play vamp and easily fail all 4 tests (in hard or expert, there is no +1). After you end your turn, play Lifeline to get 4 more actions. You can double double the vamp to get 8 actions (Im not sure if you can double lifeline or not).
Fun combo 2 : Since you can decide the skill test order, you can fail first to play Grit Your Teeth, and get +1 in other 3 skill tests.
Fun combo 3 :Dirty Fighting and British Bull Dog--- ①Play Vamp, test to fail and show your bulldog. ②Test to autoevade the enemy, and triggers dirty fighting to shot with bulldog, deals 2 dmg. You got +2 in attack since the enemy is exhausted. ③Test other 2 skills. You still got +2 since the enemy is exhausted.