BUILD CHALLENGE: The best Cohort Evar lvl 10

[Tim Proctor]

NPC stats, does not have to be humanoid, allowable books:

Players Handbook
Players Handbook II
Dungeon Masters Guide
Dungeon Masters Guide II
Complete Adventurer
Complete Arcane
Complete Champion
Complete Divine
Complete Scoundrel
Complete Warrior
Unearthed Arcana
D20 SRD (no Psionic crap)
CityScape
Complete Scoundrel
Dragon Magic
Dungeonscape
Miniatures Handbook
Races of Destiny
Races of Stone
Races of the Dragon
Races of the Wild
Spell Compendium
Arms and Equipment Guide
Manual of the Planes
Heroes of Horror
Heroes of Battle
Planar Handbook

[Biffoniacus_Furiou]

1. Obtain a Planar Cohort via Thaumaturgist (http://www.d20srd.org/srd/prestigeClasses/thaumaturgist.htm) (character level 12, which is what's required for a level 10 cohort anyway)
2. A Ghaele Eladrin (http://www.d20srd.org/srd/monsters/ghaele.htm), while having no listed level adjustment and is thus normally ineligible to serve as a cohort, can be called via Planar Ally and is thus eligible to serve as a Planar Cohort.
3. Your cohort can cast spells as a Cleric 14, use Charm Monster, Hold Monster, and many other spell-like abilities at will, and has the melee combat capability equal to a Fighter 10 but with exceptional ability scores and tons of immunities and other defenses, with a lot of high skill checks piled on for good measure.
4. This is all possible using only the three Core Rulebooks.

[Jack_Simth]

1. Obtain a Planar Cohort via Thaumaturgist (http://www.d20srd.org/srd/prestigeClasses/thaumaturgist.htm) (character level 12, which is what's required for a level 10 cohort anyway)
2. A Ghaele Eladrin (http://www.d20srd.org/srd/monsters/ghaele.htm), while having no listed level adjustment and is thus normally ineligible to serve as a cohort, can be called via Planar Ally and is thus eligible to serve as a Planar Cohort.
3. Your cohort can cast spells as a Cleric 14, use Charm Monster, Hold Monster, and many other spell-like abilities at will, and has the melee combat capability equal to a Fighter 10 but with exceptional ability scores and tons of immunities and other defenses, with a lot of high skill checks piled on for good measure.
4. This is all possible using only the three Core Rulebooks.

To call a planar cohort, the thaumaturgist must cast the relevant spell, paying the XP costs normally. It takes an offering of 1,000 gp × the HD of the creature to convince it to serve as a planar cohort, and the improved ally class feature can’t be used to reduce or eliminate this cost. The planar cohort can’t have more Hit Dice than the thaumaturgist has, and must have an ECL no higher than the thaumaturgist’s character level -2. (emphasis added)

Anything without an ECL is unavailable, as you can't compare a number to an em dash.

[dspeyer]

What is your character? What do you want your cohort to do for you?

[Tim Proctor]

Not for anything specific, just trying to see what brilliant ideas people come up with.

[Biffoniacus_Furiou]

(emphasis added)

Anything without an ECL is unavailable, as you can't compare a number to an em dash.

As I already said, it's typically unavailable as a cohort due to LA: —, but specific trumps general and you can specifically get anything that can be called via one of the Planar Ally spells. That means its LA nonability provides no modifiers to its ECL, and you only use its character level (HD + class levels) as its ECL, which must be two below your own character level.

[dantiesilva]

a dragon planar dragon if there is one in any of those books

[Seerow]

Wizard 10.