What CR is this?

[kengar]

I don't normally do these kinds of foes, but wanted to try something different:

I figured him at about CR13, am I close?

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Shadowscream

Fiendish Large Monstrous Hunting Spider , Rogue3/Sor4, AL CE

HD 9d8+4 (+3d6+4d4+7) 90
Init: +4 (DEX)
40', 20' climb
AC: 16(20*) (-1 size, +3 DEX, +4 natural, *+4 Mage Armor)
Bite +7/+2, melee. 1d8+3 & poison
Wand of Fireball, (5th Level, 22 charges) (5d6)
+2 Medium Punching Dagger of Frost (+9/+4) 1d6+4/x3 +1d6(cold)
[+2d6 Sneak Attack]
10'x10'/5'
Poison, Web
Cold & Fire Resist 15
DR 5/+2
Darkvision 60'
SR 9
Fort +6 Reflex +7 Will +4
STR 15 DEX 18 CON 12 INT 12 WIS 10 CHA 14

Climb +20 Hide +16 Jump +10 Spot +10 Move Silently +15 Search +8 Bluff +8 Spellcraft +10 Knowledge (Arcana) +9
Languages:
Elvish, Common, Draconic, Infernal

Feats: Dodge, Mobility, Spring Attack
Poison:
Fort. DC16 1d6 STR/1d6 STR

Spells (6/7/4)
Cantrips:
Detect Magic, Read Magic, Ghost Sound, Dancing Lights, Flare, Ray of Frost
1st-Level:
Mage Armor, True Strike, Jump
2nd-Level:
Invisibility

 

[kengar]

*bump*

 

[Geocorona]

I came up with an average of 77 hps and a CR of 8 (possibly as low as 7 and as high as 10).

 

[kengar]

I came up with an average of 77 hps and a CR of 8 (possibly as low as 7 and as high as 10).

With 9 "creature" HD, a fiendish template AND 7 character levels? Not to mention the magic items. I must confused how to calculate these things if that's right.

 

[Geocorona]

A CR of 8 means 4 8th-level characters should be challenged by one of these creatures, but would probably defeat it without any deaths to the party. It has a wide-shape face/reach (10x10/5) so all characters can easily flank it. Even though it has extra character levels, it's still only one creature and can execute only so many attacks per round--those character levels can't act as independent creatures. With the mage armor and the wand of Fireballs, you might be looking at a 9 or 10, but not if the characters had similar toys. Playtesting is the only way to tell for sure.

Edit: I reran the CR calc giving the monster 2 extra "specials" to double-weight those two magic items, and it came up as a 9. I use a different formula for calculating CR than the Dragon version. That version usually produces inflated CRs above CR 5.

 

[kengar]

thanks