Monster Advancement and stacking resists / DR

[setzer9999]

When a monster is advanced by a template, such as a summoned monster being advanced by a Celestial template, does it add (stack) resits and DR onto any it had before?

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For example, a Lantern Archon is already immune to electricity so that is moot so I'll only focus on the DR part for this example. It already has DR 10/evil. Does it gain a separate DR entry so it has two different types of DR then?

Does
DR 10/evil;
become
DR 15/evil or --;
or
DR 10/evil and DR 5/--;
?

If it's the latter, what do you do in the case that that creature is hit by a weapon that does not ignore all DR, but is evil? What happens if the attack is both not evil and does not ignore DR?

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Another example would be an Bralani Azata. To not muddy the waters with the above example, I'll just focus on the resists part only.

Does
Resist cold 10, fire 10;
become
Resist cold 15, acid 5, electricity 5, fire 10;
or
Resist cold 10, acid 5, electricity 5, fire 10;
?
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[Quantum Steve]

DR never stacks.

In this case, since the DRs are both DR/evil, the better of the two would take effect.

If the DRs were different, say giving DR 10/evil to a creature with DR 5/silver, whichever one was better would take effect. If you were to overcome one, but not the the, the other would still be in effect. An non-silver Evil-aligned weapon would overcome the DR 10/evil but not the DR 5/silver so damage would be reduced by 5.

[setzer9999]

Quantum Steve wrote:

DR never stacks.

In this case, since the DRs are both DR/evil, the better of the two would take effect.

If the DRs were different, say giving DR 10/evil to a creature with DR 5/silver, whichever one was better would take effect. If you were to overcome one, but not the the, the other would still be in effect. An non-silver Evil-aligned weapon would overcome the DR 10/evil but not the DR 5/silver so damage would be reduced by 5.

Thanks! I guess that would apply to the energy resist also, I know it doesn't 'stack' but I didn't know if it "added"... slightly different concept, but I'm guessing it doesn't add either.

I misread the Celestial creature template table for DR anyway, seeing a -- in the table, I mistook that to mean DR/-- but if I looked more carefully I would have seen that that meant that creatures of that HD value got NO DR at all :P whoops. Still, what you said about DR was helpful, thank you.