a few questions about adding levels to monsters

[Olive]

ok:

1) if you add 10 levels of a +1/lvl spellcasting prc to a monster that casts as a 18th level sorc., then it casts as a 28th lvl sorc. doesn't it? and gains levels accordingly?

2) if a prc gives damage reduction 20/+1 to a character at 10th level, and the creature already has damage reduction 20/+2, then what happens?

 

[gpetruc]

I'll try to answer to your questions (not fully sure of the answers, anyway)

First with the easy one:

if a prc gives damage reduction 20/+1 to a character at 10th level, and the creature already has damage reduction 20/+2, then what happens?

Just keep the better one (20/+2)
The only exception are those DR like the barbarian or the Dwarven Defender (X/-) that stack together and so (2/-) plus (4/-) becomes (6/-)

f you add 10 levels of a +1/lvl spellcasting prc to a monster that casts as a 18th level sorc., then it casts as a 28th lvl sorc. doesn't it?

Well, it depens on what you intend for "casts as a 18th level sorc". If those are marked as "spells" in the MM I'd say yes, while if those are "spell-like abilities" I'd say no.

and gains levels accordingly?

If you mean if it gets access to more spells/higher level spells, probably the same as before (and so the answer is Yes only if those are called "spells" and not "spell-like abilities")

 

[Murrdox]

For example - if you're talking about an Ogre Mage, who has the ability to cast Cone of Cold as a level 10 sorcerer once per day (dont' remember the exact level ), and then you give it more sorcerer levels... he gets all the sorcerer abilities of whatever sorcerer level you make him, AND the exact same cone of cold ability. Because the cone of cold is a spell-like ability, it will never improve, no matter how many levels you give him.

NOW, if you're talking about a DRAGON... say a gold dragon, who actually has a CASTER LEVEL opposed to the Ogre Mage, who just has a spell-like ability. Say his caster level is listed as 5 for his age group. You can give this gold dragon sorcerer levels on top of the caster level listed for him. He's no longer caster level 5, he's whatever caster level you make him depending on how many levels of sorcerer you want to grant him (note that the dragon's spell-like abilities will still never change)

 

[Olive]

i'm actually talking about an earth wierd (from MM2), with levels as alienist. he has special ability 'spells' which says that he cast spells as an 18th lvl sorc., not spell like abilities with a caster level of 18 for working out save DCs.

thanks for the help.