Have a switch nearby. When activated, the obelisk will flash different colors in the appropriate order. The player can then attack the obelisk, triggering the wisps of different colors, which must be attacked/clicked on in the right order. Repeat three times with an increasing number of color changes. Additionally (or as a separate, hard mode puzzle with identically-colored wisps), have a different musical note/distinctive sound play alongside a color change, both for obelisk and wisps.
The wisps appear. One has a special effect played on it (exclamation point, Detonate...) then all circle around the obelisk. The player must find the wisp that had the special effect earlier. Include several variations in movement patterns (crisscrossing, switching directions...). Once one is found, this process is repeated n times with n-1 wisps.
Give the wisps Mirror Image. The player has a limited amount of time to kill the real one. (If it is possible through character customization to have no multi-target spells, hide an item with Dispel Magic somewhere in the dungeon).
Have a 6x4 grid of black wisps set up. Before the puzzle starts, the wisps change color in pairs before reverting to black. The player must then select matching pairs. Either he matches them all, or four pairs must be found in the right order, with the grid resetting itself when a matched pair is found.
In case of failure, the puzzle resets, and minor enemies appear. No more than four or five, and defeatable in a few seconds.
