This is somewhat difficult to recreate, but you can take advantage of falling through the world in order to kill NPCs without being attacked.
There are certain areas all around Telon where you can obviously see where two textures meet. If you run in to them at a certain angle, you will fall between the textures. This is most easily done in rivers as there are lots of "holes" that you can fall in to get under the world.
While under the world, you can run about freely and target NPCs using TAB. From there, you can cast spells on them without a problem. The mobs will stand over top of your location, but they cannot hit you.
There are certain areas all around Telon where you can obviously see where two textures meet. If you run in to them at a certain angle, you will fall between the textures. This is most easily done in rivers as there are lots of "holes" that you can fall in to get under the world.
While under the world, you can run about freely and target NPCs using TAB. From there, you can cast spells on them without a problem. The mobs will stand over top of your location, but they cannot hit you.