Magic affecting the choice to stand and fight or run.

[fredramsey]

The T-Rex would only run from the fireball or lightning bolt if it was hurting him enough to make him think of going after easier prey, in my opinion. He might be confused, unused to the sensation, but if hungry enough, it would just make him mad...

 

[fusangite]

Lots of high CR critters have extremely low intelligence. Many seem as if they would leave most encounters at a display of showy magic or stinging might.

How do you justify not having the Tyrannosaur run at first sight of lightning or a fireball? Do you ever have low INT monsters fight to the death outside of a "Lair" scenario?

I think the main issue here is what the creature is used to. For instance, I cannot imagine any creature in a Forgotten Realms campaign fleeing magic except for the precisely opposite reason (it knowing what the particular spell was and had had a bad experience with it).

In the case of a dinosaur and a fireball, I would probably have it run, not because there was something strange about this particular Fireball but simply because natural fire is scary and dangerous when it is very hot and there is lots of it.

Also recognize that many spells replicate natural phenomena; in the event that a spell resembles a particular phenomenon, like Call Lightning for instance, I would use the creature's reaction to the natural phenomenon.

 

[diaglo]

I think the main issue here is what the creature is used to.

like deer, squirrels, bears, etc... in national parks that will eat food offered by picnic/campers. vs. the same animal out in the wild.

or the Gods Must Be Crazy example of a Coke(tm) Bottle falling from the sky.

or the PCs coming up against their first... X monster without prior knowledge of just what it can do or if it will eat them.

 

[Tonguez]

Creature is just out walking (not hungry) - will flee at 75% HP

Creature is hunting - will flee at 50% HP

Creature defending its Lair - will flee at 25% HP

Creature defending its Young - will flee at 5% HP

Multiple Creatures - minus 20% HP before they flee (eg a pack of wolves out hunting will flee at 30% HP)

I also use a Morale system for intelligent humanoids/giants etc
Attack roll - Creature AC = Morale Modifier
eg Attack roll 21 - AC 16 = 5 mod

Morale DC = base + mod (0 + 5) = 5 (defending creature makes Will save v DC 5)
Base starts at 0 but increases due to 'Phobia' and other mods (which includes flashy shows of magic)
Phobia minor base DC 5, medium DC 10, major DC 15

eg Dragons always have a Phobia rating of 10 (they are naturally scary), a character who has in the past been panicked by a giant spider might have a minor Phobia to spiders etc etc

 

[alsih2o]

I also use a Morale system for intelligent humanoids/giants etc
Attack roll - Creature AC = Morale Modifier
eg Attack roll 21 - AC 16 = 5 mod

Morale DC = base + mod (0 + 5) = 5 (defending creature makes Will save v DC 5)
Base starts at 0 but increases due to 'Phobia' and other mods (which includes flashy shows of magic)
Phobia minor base DC 5, medium DC 10, major DC 15

This looks cool, but can you clarify a bit for those of us with learning disabilities or a profound case of the stupids?