Max AC- 16
Most 7th Sons of a 7th Son are born with strange omens of their birth. Falling stars, murders of crows outside the home when they are born, an icy cold placenta, and so on. For humans, a 7th Son of a 7th Son is considered lucky and specially destined for greatness. Other races may have different numbers or even genders depending on the warriors; Elves find the 3rd Son of a 3rd Son special, where as the Goblins may find the 21st Son of a 21st Son. Matriarchal societies like the Gnolls will instead favor the 4th Daughter of a 4th Daughter and so on. This power may be even more strict in some culture, requiring an unbroken lineage with no daughters/sons of the opposite gender.
7th Sons are said to be special. Guided by destiny and empowered against magical creatures and spirits alike. While not necessarily always good or honorable, Seventh Sons are said to have special powers against the undead and demons, and are said to have skills with magic, at least in regards to the healing arts. You are a little bit like a paladin.
One of the main powers of a Seventh Son is their special eyes- to see through glamours. You are immune to the mind effecting abilities of creatures and spells cast by creatures equal to your level as HD or less. You get advantage on saving throws versus illusions if the source of the illusion had HD equal to your level or less. For spells or abilities with multiple effects, you are only immune to the mind affecting portion and are normally harmed or hexed by the rest.
You gain +1 to hit at level 3, 6, 9, and 10.
You gain +1 damage to attacks at levels 5 and 9. You also deal +1 damage with magic rods or wands at level 7. You can use wands and scrolls at this level if you couldn't already.
You have healing hands. You can attempt to heal someone without using any first aid supplies once per day per level- equivalent to a magic spell, just takes an exploration turn. You also heal +1 more health when you do heal someone this way every even level.
Your presence inspires others to holdfast against darkness. Hirelings under your command get +1 to their saves and morale checks versus supernatural fear and panic if your level matches or exceeds the HD of the offending force. Treat your level as one higher for Turning Undead. At level 4th level, you may draw a poison into yourself by sucking on the wound; the character harmed by the poison transfers it to you, and all the remaining damage or negative effects of the poison harm you instead.
At 10th level, you become a Son-Of-Omen and fully unlock your mystical abilities. Your powers include the sight-beyond-sight, granting you a once per adventure view into the future or past, as long as you have time to meditate on the event in question. The timeline you can see is expansive, but the mythic past and far future are beyond your sight. Secondly, your ability to heal also improves; you never need healing supplies to heal someone, and you can also draw level drain from another character into yourself, and the same goes with curses and other mystic maladies.
As a secondary effect; you become totally invisible and silent to demons and the undead. You could walk through hell unmolested. These beings refuse to notice your presence, even if told by other beings that can sense you. This effect lasts until the next time you attack a creature of darkness, in which case this power ends permanently.