Q182: Infernal bargainer lets me have +2HD on the monster when casting
planar ally. Thaumaturgist can have a planar cohort called by planar ally spell with the limitation -2 ECL.
So for example cleric 7 / thaumaturgist 5 = ECL 12.
Thus the planar cohort would be ECL 10 at most. Or is it HD 12? Or HD14 with infernal bargainer?
Is this interpretation correct? So no
Osyluth as a cohort.
See also
monsters as races.
Infernal Bargainer
[spoiler]
Type: General
Source: Races of Faerûn
You are comfortable making deals with powerful entities from the Lower Planes.
Prerequisite: Outsider
Benefit: Whenever you cast commune, contact other plane, legend lore, or vision, you gain +2 caster level because you are known to the entities answering your entreaties.
Whenever you cast any planar binding or planar ally spell, you can call an evil creature 2 HD higher than normally allowed. Any evil creature caught in a planar binding trap you create has a -2 penalty on all attempts to escape.
[/spoiler]
Thaumaturgist:
Planar Cohort[spoiler]
A 5th-level thaumaturgist can use any of the planar ally spells to call a creature to act as his cohort. The called creature serves loyally and well as long as the thaumaturgist continues to advance a cause important to the creature.
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.
A thaumaturgist can have only one planar cohort at a time, but he can continue to make agreements with other called creatures normally. A planar cohort replaces a thaumaturgist’s existing cohort, if he has one by virtue of the Leadership feat.
[/spoiler]