When facing an abomination with a terror rating, when is the terror check triggered in the encounter? Is there only one check per encounter?
The terror check is triggered when the combatants first become aware of the abomination. There is only one such check per encounter.
This is excluding certain Edges (Nerves of Steel, maybe - I might be getting that name confused with an "All Flesh Must Be Eaten" Quality) that can allow a player to forgo the check.