I liked Ulduar because you selected the difficulty by your actions in the game world and not with the game options. This felt more immersive.
Here is an example of how this could be done in a single player RPG:
You have to kill a general in an army base. If you charge through the front door you will face the general and 4 groups of soldiers at once. This is very difficult but it can be done. If you do not want to fight the whole base at once you can do some things:
- Sneak into the base without being seen.
- Give fake orders to one group. They will leave the base. (You need to find some items to craft the fake orders.)
- Poison the food in the kitchen. One group will fall asleep. (You need poison and you have to enter the kitchen without being seen. They will not eat when they see an intruder messing with their food.)
- Deactivate the alarm. It will take longer until enemies find out whats going on. (you need to find the alarm and a deactivator without activating the alarm)
- The third group has their room behind the room of the general. If you attack him they will come at once. You can get to their room from the back door and start fighting them. The general and his group will will enter the room and join combat after 3 turns (1 turn if you did not deactivate the alarm).
When you do all these things, you have to fight only 2 groups and one of them will be weakened (or even dead if you are good) when the second one ( plus boss) arrive.
This means, if you want to have an easy fight you have to do lots of things. These things can go wrong if you are not careful. If you make a mistake you have to fight in a position where the enemy has an advantage.

Prof. Dr. Dr. Mad S. Tist

World leading expert of artificial stupidity.
Because there are too many people who work on artificial intelligence already