Thank you all so much for your help! I checked the Eldritch Scoundrel and I think it has too little skill points and sneak attack, but maybe I'm mistaken. I'll be a little more specific about the whole situation:
If I get access to any sort of spellcasting or pact magic, I'll receive the following spells:
Cantrip: encode thoughts, mage hand.
Lvl 1: disguise self, sleep.
Lvl 2: detect thoughts (I can use this with encode thoughts to take memories out of a Helpless target and sell or erase them, I can't risk them passing the will save), pass without trace.
Lvl 3: gaseous form, meld into stone, nondetection (these would be great to have but not indispensable).
Lvl 4: arcane eye, freedom of movement
Lvl 5: modify memory
I suppose I can be a sorcerer, I mainly want the special spells I'll be receiving.
The DM allowed me to be a rare human shapeshifter, he's merging some stuff but he's willing to accept modifications for the story. I can change to animals and magic beasts but with no abilities (I think I have to invest ranks in fly if I want to escape when they find out about me).
The party currently thinks I'm a Goblin fighter. They underestimate the goblin which is useful but the DM always lets them roll for stuff I do. We have DPS in the party, so it doesn't matter me not hitting, I just say "oops, rolled a 2 for attack" and they don't even check. Why would someone cheat not to do something anyway, right?
And the only reason I chose rogue is because of the skill ranks (and let me correct this: The vampire has 34 perception. 34!!)
My current build is with the stats I mentioned, I have 10 ranks in: bluff, diplomacy, disable device (I plan on doing some infiltration, maybe I'll erase one NPC's or PC's memory), disguise, intimidate, perception, sense motive, sleight of hand, stealth.
Feats: Combat reflexes, dodge, two weapon fighting, greater two WF, improved initiative. And as my talents, I have [lvl2] minor magic (detect magic), [lvl4] mayor magic (vanish), [lvl6] convincing lie, [lvl8] follow clues, [lvl10] familiar [owl+3 perception]. I got for being a rogue trapfinding, evasion, trap sense+3, uncanny dodge and improved uncanny dodge. I have a Fog Cloud wand just in case they discover me, this would help me escape. My owl is most of the time guarding far away, I can't afford the freaking 34 perception vampire seeing it. I was planning on getting an Improved Familiar at level 11. My current sleight of hand and stealth are 19. With this build I get access to lvl 2 spells, that's what the DM allowed me. What do you guys think? Also, I can take the memories out of my owl to see what it saw.