Please help me with adjusting CR

[Zarnam]

Greetings

I am currently making a unique creature and I thought not to give it any spellcasting class levels, but instead give it abilities to cast spells as a 20th level sorcerer and the Item Master ability which some Fiend Lords possess, that enables the use of some spell completion items and such.

What CR increase would you apply for those two abilities ??

Thanks

 

[shilsen]

One can't really apply a blanket CR gain from the listed abilities without knowing more about the creature. While the ability to cast spells as a 20th lvl sorcerer is very valuable, it's a lot more valuable to a creature which has a lot of durability, since it can last long enough to benefit from the spellcasting. Whereas applying it to a garden variety troglodyte doesn't do as much, since even with the spellcasting ability it is likely to go down very easily.

In short, more info is required.

 

[Zarnam]

Well, this creature is supposed to be an Outsider with about 20-25 hd something akin to a Solar...