I know this thread is over a year old, but I have a question or two about this.
First off, "meeting a monster for the first time" is only _one_ reason for a Terror save. Clearly, many monsters are meant to invoke fear any time you meet one, not only the first time. This becomes obvious when you look at the Demon Killer feat.
I quote: "Each time you defeat a new monster, you become immune to the terror effect of that creature, if any".
This would make no sense if all monsters would cause terror only on first sight.
So this would mean that the Barbarian can fly into a Rage any time (once per day) he encounters a monster with fear effect, or any other source of Terror.
However this gets me to a question:
Isn't the Demon Killer feat rather counter-productive for a Barbarian? Of course +2 against Terror is good, but if he is immune, he doesn't need to make a save, thus he cannot use his Crimson Mist ability, unless you make a house rule.
Maybe change them as follows:
Crimson Mist: if the Barbarian succeeds his Will save against Terror, he can CHOOSE to fly into a rage.
Demon Killer: Will saves versus Terror effects of a creature type that has previously been defeated automatically succeed.
(So a Barbarian can choose whether to activate Crimson Mist against a monster type he has previously encountered)
What do you think?