On one side of this gestalt build is a witch with the Winter Witch and Ashtifah archetypes, later going into the Winter Witch prestige class.
Eventually, this will turn you into a full arcane caster specialised in cold spells with the ability to tear through cold resistance and immunity.
To pursue my idea you take this hex-
Frozen Caress (Su) Whenever the winter witch casts a touch spell, she can infuse the magic with cold as a swift action. This grants the spell the cold descriptor, and adds 1d4 points of cold damage to the spell’s effect. If the touch spell allows a saving throw, a successful save negates this additional cold damage.
You get this ability at level 2-
Ghostwalk (Su): Starting at 2nd level, as a move action after using a hex, an ashiftah can become invisible as per vanishAPG and can then take a 5-foot step. Using ghostwalk doesn’t provoke attacks of opportunity.
This ability replaces the hex gained at 2nd level.
And you take this feat, the hex being Slumber.
Hex Strike (Combat)
Chanting and cursing, you put a hex on your enemy as part of your unarmed strike.
Prerequisite: Hex class feature, Improved Unarmed Strike.
Benefit: When you gain this feat, choose one hex that you can use to affect no more than one opponent. If you make a successful unarmed strike against an opponent, in addition to dealing your unarmed strike damage, you can use a swift action to deliver the effects of the chosen hex to that opponent. Doing so does not provoke attacks of opportunity.
Special: You can take this feat multiple times. Each time you take it, you apply it to a different qualifying hex.
On the other side, you take 4 levels of Slayer, Executioner Archetype. And one level of Magus, Esoteric Archetype. This gives you spell strike on unarmed strikes from one level of magus, which reads-
At 2nd level, whenever a magus casts a spell with a range of “touch” from the magus spell list, he can deliver the spell through any weapon he is wielding as part of a melee attack. Instead of the free melee touch attack normally allowed to deliver the spell, a magus can make one free melee attack with his weapon (at his highest base attack bonus) as part of casting this spell. If successful, this melee attack deals its normal damage as well as the effects of the spell. If the magus makes this attack in concert with spell combat, this melee attack takes all the penalties accrued by spell combat melee attacks. This attack uses the weapon’s critical range (20, 19–20, or 18–20 and modified by the keen weapon property or similar effects), but the spell effect only deals ×2 damage on a successful critical hit, while the weapon damage uses its own critical modifier.
At level 4 Executioner gives you-
Painful Strike* (Ex): At 4th level, a Sczarni executioner automatically gains this talent. Sczarni executioners are trained to cause excruciating pain when striking targets, often leaving them reeling in agony or completely incapacitated as they slowly bleed out. A creature that takes sneak attack damage from a Sczarni executioner must make a successful a Fortitude save (DC = 10 + 1/2 the Sczarni executioner’s class level + his Intelligence modifier) or become sickened for 1d4 rounds. This ability alters the slayer talent received at 4th level and replaces swift tracker.
For race, you want one with a good int and natural attacks. Suitable is a Changeling with the Witchborn and Kitsune Parentage alternative racial Traits.
On a 25 point build that will give your character-
With 2 claws and one bite all doing 1d4 + str mod.
Now how this is intended to work.
First sneak up on an enemy and study them for studied target using ghostwalk. Say you are level 5 and your target is a humanoid.
You then as a standard action cast a touch spell, say touch of blindness. You then add frozen caress as a swift action and hex strike as a move action. Then belt the target.
The effect will be-
1d4 bite damage
+2 from str
+3 from studied target
1d6 precision damage
And the target must save vs blindness for 1 round plus 1d4 cold damage, then make a second save against being put to sleep for 5 rounds and finally a third save vs painful strike or be sickened for 1d4 rounds.
You have 5 rounds of touch of blindness in total, 4 more. In these rounds you can make full attack actions which will be 3 attacks as above without the precision damage and slumber hex.
This should be enough to allow people to see what the character is intended to do.