Rogue build based on the Dark folk Creatures

[Reprimand]

So I wanted to use the unchained rogue to emulate the dark stalker from bestiary 1. I want to use Gloom Magic and see through darkness and poison use for theme in and flavor but they also let me get quite a few sneak attacks off early on. When gloomy magic isn't an option circling Mongoose and flanking will have to do.

How can I improve on this concept without dropping the theme of the character?

My stats are 15 15 15 12 19 20 our dm had us roll 8+1d12 for all stats which I've never seen before but it worked out okay. We are starting at 4th level.

Planning on human with the skill focus bonus feats alternative racial trait since I plan to take skill focus Stealth for hellcat Stealth and Dampen Presence anyway.

My current feat talent list looks like this:

Roland Redgrave Human Male

Rogue 4

30+(1d8+2)

12 str
22 dex (20+2)
15 con
15 int
15 wis
20 cha (19+1)

Stealth max (skill focus)
Sleight of hand max
Sense motive max (skill focus 16th)
Perception max (skill focus 8th)
Bluff max
Diplomacy max
Intimidate max
Linguistics max
Disguise max
Climb (2 rank)
swim (2 ranks)
escape artist (2 ranks)
acrobatics max
Knowledge local leftover ranks?
Craft Alchemy max?

Feats:
H: Skill Focus : Stealth
B: Weapon Finesse
1: TWF
3: dodge
5: mobility
7: spring attack
H8: Skill Focus: Perception
9: Circling Mongoose
11: Improved TWF
13: Hellcat Stealth
15:* Dampen Presence
H16: Skill Focus: Sense Motive

Talents
2 - Poison Use
4 - Minor Magic (Message)
6 - Gloom Magic
8 - Greater Gloom Magic
10 - See In Darkness
12 - Double Debilitation
14 - Improved Evasion
16 -
18 -
20 -

Skill unlocks?
5 - Acrobatics
10 - Sense Motive
15 - Craft Alchemy
20 - Stealth?

Note the dm is letting me take rogue Talents the unchained rogue does not normally have access to. I think I want to sink a feat into master alchemist or spend a skill unlock on craft alchemy.

[Pyromancer999]

Shadow Walker archetype should help the general concept. There's also Gloom Chemist for Alchemists, if you want to go that direction, and your DM will let you take the Rogue talents you want in place of Discoveries.

[Reprimand]

Basically I just wanted to get as close to playing a dark stalker without playing the actual race and having a level adjustment.

I was hoping to get some idea on how I could Mae this more effective without changing the class or going for homebrew beyond what I've stated. I am well aware of alchemists, investigaters, slayers and many many more but I wanted to play a rogue darkness related powers. For the Record I am using the unchained rogue. Is there a more efficenct order zip can take my feats in and so on? Better feats? Skills that fit the theme of the character better? I'm considering swaping wisdom and cha because I'm moving more toward an assassin than a face which was the original idea but I switched while writing up the character.

[Florian]

Swap Human with Fetchling and use the Shadow Scion U-Rogue archetype.

[inuyasha]

I know this isn't entirely helpful, but are you going to replicate the fact that Dark Stalkers explode? I always found that amazingly entertaining.