Win at a cost: Say I need 5 successes to open a door. When I roll I get: 4 successes and 4 failures. None of the dice rolled came up a natural 1(skull). I could open the door, but set of the security alarm as a result of not having enough successes. Same situation, but this time I have 3 successes and and 5 failures(no 1s or Skulls). This time I open the door, but the alarm goes off and I’m caught on video breaking and entering. The higher the margin of failure, the worse the cost to win the test.
_beastial Failure: I need 5 successes to open the door. This time I roll 4 successes 3 failures and 1 _beastial Failure. So I kick the door open in a fit of rage, and remain paranoid for the remainder of the scene. I know that someone had to notice my actions, now where are they, and when will they be coming for me…
Win at a cost is a great way to add flavor to checks and tests without making characters do the same thing over and over again. Provided that they have rolled at least one success.
_beastial Failure on the other hand is literally the character losing control of their beast for a small moment in time. A willpower reroll is the only way to negate a _beastial Failure. The roll of a _beastial Failure overrules the use of win at a cost.