As an alternative, we could allow the dispel turning and bolster undead part of Subjugate Undead take the place of the aura. I kind of like that.
I prefer an Aura approach.
Bolster Undead has a lot of differences to how the original power works. It requires a standard action, has a limited range (60 feet) and duration (10 rounds) and requires line-of-effect.
The "Aura" is continuous and requires no action on the Master's part, covers an area large enough to encompass an entire mausoleum complex containing scores of undead, and works through rock and earth (since most of the undead are not in the same chamber as the Master).
It's more like an
unhallow effect than a bolster undead action.
But, if we go with the profane aura or whatever we call it, I wouldn't make the bonus tied to the number of bone tyrants explicitly but rather through the positive levels the master has.
That chart was copied from the original adventure, I wasn't planning on adapting it for our conversion.
If we make the "turn resistance bonus" equal to half the Master's Subjugate Undead level, then it'll exactly match the Turn Undead modifiers in the table.
E.g. if it loses two minions and gains 2 positive levels, its "effective cleric level" goes from 11th to 9th and it grants a +4 turn resistance bonus, the same as the "4 minion" row on the table.
How's this.
Turning Check Version
Unhallowed Aura (Su): A bone tyrant master that has been bound to an unholy altar causes that altar to radiate an effect similar to the
unhallow spell. The person summoning the bone tyrant sets the size and shape of the unhallowed ground when they bind the tyrant to the altar. Its maximum size is a radius of 100 ft. plus 10 ft. per caster level of the summoner.
All turning checks made to turn undead within the Unhallowed Aura take a profane penalty equal to half the effective cleric level of the master's Subjugate Undead ability. Remember that the master gains positive levels if any of its minions are destroyed (see Minion Dependence), which will lower its effective cleric level. For example, a typical master has a Subjugate Undead level of 11, so radiates a -5 turn check penalty. If it loses 3 minions it gains 3 positive levels, weakening its Subjugate Undead to 8th level, for -4 turn check penalty.
Note that the Unhallowed Aura's turn undead penalty does not stack with the -4 turn undead penalty of an
unhallow spell, since both are profane penalties.
Nonmagical barriers do not obstruct an Unhallowed Aura. A
hallow spell will block the effects of the aura, while a
protection from evil or
magic circle against evil spell will weaken the Aura by 2 (e.g. a -4 turn undead penalty becomes a -2 penalty).
Turn Resistance Version
Unhallowed Aura (Su): A bone tyrant master that has been bound to an unholy altar causes that altar to radiate an effect similar to the
unhallow spell. The person summoning the bone tyrant sets the size and shape of the unhallowed ground when they bind the tyrant to the altar. Its maximum size is a radius of 100 ft. plus 10 ft. per caster level of the summoner.
All undead within the Unhallowed Aura gain a profane bonus to their turn resistance equal to half the effective cleric level of the master's Subjugate Undead ability. Remember that the master gains positive levels if any of its minions are destroyed (see Minion Dependence), which will lower its effective cleric level. For example, a typical master has a Subjugate Undead level of 11, so radiates a +5 turn resistance Aura. If it loses 3 minions it gains 3 positive levels, weakening its Subjugate Undead to 8th level, for a +4 turn resistance Aura.
Nonmagical barriers do not obstruct an Unhallowed Aura. A
hallow spell will block the effects of the aura, while a
protection from evil or
magic circle against evil spell will weaken the Aura by 2 (e.g. a +4 turn resistance becomes +2 turn resistance).
