Occult:

This magic comes from the occult tradition, calling upon bizarre and ephemeral mysteries. Anything with this trait is magical.

A creature with this trait is primarily constituted of or has a strong connection to occult magic.

Thrall:

The mindless undead you can create as a necromancer are called thralls. Spells or abilities that create thralls have the thrall trait.

Thralls

A thrall is a level –1 creature with the mindless and undead traits. It's not a minion, nor does it have the summoned trait. It has 1 Hit Point and is immune to bleed, death effects, disease, mental, and poison. Thralls automatically fail all checks, and any check made against a thrall automatically succeeds. They can take actions only when commanded to by a grave spell or necromancer ability. A thrall is temporary and is destroyed after 1 minute if no other duration is listed.

You choose whether a thrall is Small or Medium when you create it, and you must create it in an unoccupied space or the spell or ability that created the thrall fails. A thrall can contribute to flanking as though it were able to make melee unarmed Strikes. Thralls can't hold their ground—a creature can move into a thrall's space as though it were unoccupied. The thrall's space is difficult terrain, and the moving creature can automatically push the thrall into an adjacent space that's not in its path.

A thrall has a Speed of 15 feet unless otherwise noted. You can use the Command a Thrall action (see below) as long as you have at least one thrall. When you Command a Thrall to Strike, it makes a melee unarmed Strike using your spell attack modifier for its attack roll. This Strike uses and counts toward your multiple attack penalty. The Strike deals 1d6 bludgeoning, piercing, or slashing damage. At 5th level and every 4 levels thereafter, the damage increases by 1d6.

Command a Thrall [one-action] (concentrate, necromancer, thrall) You make one of your thralls Crawl, Drop Prone, Escape, Interact , Stand, Stride, or Strike. A thrall can take only simple Interactactions, not ones that require skill checks or complicated movements. However, they can make checks to Escape using your spell attack modifier. Escaping this way uses and counts toward your multiple attack penalty.