Has a World Baseball Classic game ever ended 12-0?
Exactly once. On March 4, 2013, Cuba beat China 12-0, and no World Baseball Classic game before or since has ended that way. When it happened it was a scorigami, the first 12-0 in league history.
That makes 12-0 the 47th most common final score out of 80 that have ever occurred in World Baseball Classic. One point away, 13-0 has happened never and 12-1 has happened 1 times.