Olgar Shiverstone
Legend
I want my all but a god of war.
Sexy, shoeless gods of war?
I want my all but a god of war.
My early experience (1e) was about 15 th ... In recent editions this feels more like 11 th....
My experience was the opposite - in 1e ca 10th level PCs could take on an M-U 18 Lich, but in 3e you had to be within a few levels, due to spellcaster dominance. I've hardly ever used high level NPC casters in 3e for this reason, they have too many obvious I Win buttons.
I say that because in my own games in the way back (1E), if you encountered a Lich, you ran. That is unless you were at the same, or higher level. There were too many spells that were save-or-die to be able to take the chance.
Since an 18th level Lich was specified in the OP I would say theres 2 answers.
1. I ran into a lich in the middle of the woods and neither side is prepared (anti-climactic yes, but just for the sake of argument) Well then I would say a 10th or 11th level is a good time to fight him and less then that should run.
2. On the other hand Lets go plunder this liches highly defended lair and send his bony butt to hell where he belongs. That because of the nature of the lich being able to make the most use of his abilities and defenses is more of a 15th level adventure for a party.