I thought that during an encounter the overlord could use his treachery for some cards in his hand. After re-reading the rule book I'm not so sure. It seems that treachery can only be used in such a way when a luitenant is present. Is this correct or did i miss a sentance somewhere?
. You can use in Lt encounters to grab either treachery cards or regular cards of the appropriate type (2 normal cards per 1 point of treachery, so 2 spawn cards for 1 monster treachery). Then before each dungeon, you get to spend treachery to modify you deck.