This card is great for most survivors, particularly those with Achilles stats like Wendy’s fight, Calvin anything or Silas intellect or willpower. Combined with Leo de Luca, quick thinking or any number of other cards can give you 4-5 turns with a giant boost stat. Also ace of rods can give you extra turn with one test at 7! Watch Wendy crush the ghoul priest, Silas Hoover up clues or laugh at an encounter 4 test. Also Ashcan Pete and Calvin can prosper plus any other char that can take the spirit trait.
Fast. Play only during your turn.
Choose one of your skills. Until the end of your turn, set the base value of that skill to 5.
This is the level 1 Will to Survive. It serves a very similar function.
Rewrite any character's stat as a 5. This is obviously great for anybody starting at 1 or 2, note that all modifiers (boosts on weapons for example) stack on top.
A 5 for a round is most useful if you can leverage it, upping to 5 for example is useful all the time, but upping isn't great unless you've got a weapon to swing.
Terrific in maps that require you to beat a specific test type on scenario cards, for example if you gotta beat x amount of tests or beat a crucial parlay.
Benefit lasts until end of turn, thereby it will never help you in the Mythos phase.
All in all this is a great card, mandatory in Calvin Wright and damn-near everybody else can use it for something, at the very least 5 is never useless.