Here you will find house rule changes to some creatures along with some explanations of the changes to creatures from previous games. Pathfinder has taken a different approach to some creatures and the differences would be known to a character in Golarion, though players may have prior knowledge which may not be accurate.
Regeneration (House Rule)
In general, creatures with regeneration have a weakness to some type of damage, here I am going to use a trolls regeneration as an example. Trolls regenerate anything but fire and acid damage.
In previous editions, the GM kept track of fire and acid damage as lethal damage and all other types as temporary damage. New editions of the rules say that fire or acid damage stop the creature from regenerating and if the creature dies by taking that lethal damage type, it's dead.
House Rule
While fire and acid stop the creature from regenerating for a time, maybe a minute for minor damage, maybe ten minutes for major damage, if the creature is left unattended, it will start to regenerate again. The fire and acid damage needs to heal normally, usually taking days, but the other damage sustained by the troll heals quickly.
To destroy a troll, after the battle is won, the corpse must be burned. It usually takes at least 5 minutes of sustained damage for a medium or smaller creature, 10 minutes for a large creature, doubling for each size category larger.
Trolls, being social and sentient creatures, often try to retrieve their fallen when running from a battle, especially if the fallen is from the same clan or tribe. Other regenerating creatures don't usually exhibit the same care for their fallen.
Drow
There is no Lolth. There is no Spider Queen. The drow houses each worship a different demon lord, and the Houses vie for supremacy in the Darklands in the same way that the demon lords vie for supremacy in the Abyss. Two Houses worshipping the same demon lord may find common ground, but each believes itself to be the true representative of their shared demon lord. Only one can be dominant.
Fiends
Demons are born of sin, and each type of demon reflects a particular sin. Since there are countless variations of sin, there are countless variations of demons. Daemons strive for the end of everything, and they represent death and destruction. Daemonic types represent different ways mortals can die, from plague to famine, to suicide, etc. Devils are creatures of corruption and tyranny.
The three types of fiends are not opposed to one another, in fact there is significant overlaps in their outlooks. There is no great fiendish conflict (no Blood War), and fiends of different types may be found working together when their natures align.
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