Jacob Marley
Adventurer
Honestly, it depends on which of the monsters is being used. In the case of basilisks and the medusa, these are monsters that are likely to leave an obvious footprint on the surrounding environment. It is more likely that the party will encounter the petrified remains of the vicitms long before they encounter the actual monster. At this point the players would receive a knowledge (_____) check and (if successful) being given the relevent information about what could have caused this, and how. The party then can choose to act in which ever way they see fit.
With nymphs it is a little different. Nymphs are less likely to have an obvious footprint on their surrounding environment, nymphs are also less likely to be openly hostile to the party. In most cases encounters with nymphs will be peaceful. The party can make their knowledge (nature) checks and (if successful) will receive the appropriate information.
Nymphs rarely initiate combat.
Bodaks and umber hulks are the most likely to attack without any fair warning to the party. In these cases initiative order becomes very important. However, as bodaks are native to evil-aligned planes and umber hulks to the underdark it is the responsibility of the party to learn about the potential threats before they enter these places and then to act accordingly.
I am willing to give the players warning through the setting but it is the players' responsibility to make use of that information and tell me how they proceed.
With nymphs it is a little different. Nymphs are less likely to have an obvious footprint on their surrounding environment, nymphs are also less likely to be openly hostile to the party. In most cases encounters with nymphs will be peaceful. The party can make their knowledge (nature) checks and (if successful) will receive the appropriate information.
Nymphs rarely initiate combat.
Bodaks and umber hulks are the most likely to attack without any fair warning to the party. In these cases initiative order becomes very important. However, as bodaks are native to evil-aligned planes and umber hulks to the underdark it is the responsibility of the party to learn about the potential threats before they enter these places and then to act accordingly.
I am willing to give the players warning through the setting but it is the players' responsibility to make use of that information and tell me how they proceed.