A Combat Encounter is a type of encounter that occurs when the Investigator begins the Encounter Phase while on the same space as a monster. The investigator must encounter every monster that shares his space, one at a time. If there are both Normal Monsters and Epic Monsters on the space, the Normal Monsters must be encountered before the Epic Monster.
The Encounter begins by making a check, plus any modifiers for Horror checks, against the monster's Horror rating. If the player's check is lower than the monsters, he suffers Sanity loss equal to the difference. If the check is equal to or greater than the rating, he suffers no damage. Some monsters use a different skill for this check, and some monsters have no result, in which case no check is rolled.
Then, the investigator rolls , plus any modifiers for Combat Encounters, against the monsters Damage rating. If this result is lower than the monster's, the player suffers Stamina damage equal to the difference. If the player's result is equal or greater than the rating, he suffers no damage. If the monster has no Damage rating, the player still rolls their check unless otherwise specified on the back on the Monster's token, but there is no possibility of Stamina loss.
Any successes the player rolls on the roll is then subtracted from the monster's toughness. If the monster's toughness reaches zero, it is destroyed and returns to the monster cup barring any change such as Tasks that collect slain monsters.
If all monsters have been defeated after the Combat Encounter, the player has their Encounter Phase, just as they would if there had been no Monsters on his space, as long as the monster didn't have a special ability that prevents this. If there are one or more Monsters remaining on the space, that player skips the Encounter Phase, and play continues to the next Investigator.
A: Less Success than the Monster's Damage: The investigator fights against a Ghoul which has 1 Toughness and 2 Damage. The investigator rolls and obtains only 1 success; as result the investigator lose 1 Health (e.g. according to monsters' stat, it deals two damage minus the number of investigator's success, thus 2 - 1 = 1), and the Ghoul die due to 1 (one) sucess, which means one damage.
B: Success Equal to the Monster's Damage: The investigator fights against a Goat Spawn which has 1 Toughness and 2 Damage.The investigator rolls and obtains 2 successes; as result the investigator won't take any damage, while the Goath Spawn will die due to 2 (two) sucess rolled by the investigator.
As with other kinds of tests Passing a Monster's / test constitutes rolling at least one success. In example:
Monster's special effect states that "if investigators Fails test he does not resolve test". Monster's Horror rating is 2 and investigator rolled 1 success on test. Investigator Passes this test because he rolled at least one success, but still loses 1 Sanity since we subtract number of successes from Monster's Horror rating and apply this number as Sanity loss. If investigator is not defeated he can now perform check as usual. On the other hand if Monster's special effect stated that "if investigator loses Sanity from test he does not resolve test", investigator will not resolve test since he lost 1 Sanity.