So hey this is the first post I've made so sorry for making it on a 4-year-old post, but I've been playing a vanilla melee mesmerist for some time and I absolutely love it.
So to start I use the criminally unmentioned divine fighting technique (Way of the Shooting Star). Mesmerists aren't proficient with starknives so I picked up the trait Tattooed mystic (human race trait) which gives it to me with a small buff to charm/compulsion saves. There are other ways of getting this but I didn't want to take a level dip. For those of you that don't know about divine fighting techniques, they are feats that basically change the way certain weapons work. In this case, the way of the shooting star, lets you use charisma for your attack and damage role in place of str or dex. This applies to both melee and thrown starknives. This lets me buff my spell casting without sacrificing offense. Starknives aren't the most appealing as far as damage or crit range but its crit modifier is x3. At level 4 you'll have access to hold person and with a x3 multiplier and the additional damage from painful stare, you can coup de grace most humanoid enemies at your cr for quite a few levels no issue.
Now I went down the Eldritch Heritage feat chain with this, it's not for everyone and the bloodline I went with may not be allowed in all games (nanite), but the benefit of adding a scaling poison to your attacks for free is nice especially if you take lethality for a bold stare. Picking a human is nice when going down the Eldritch Heritage route because of the alternate human trait Focused Study which replaces your level 1 bonus feat with Skill focus at level 1, 8, and 16 (so if you plan on taking skill focus you may as well get it two more times for free). Though if you don't want the investment I'd recommend replacing with spell focus illusion or enchantment.
Here is a simple outline of the build at level 8:
STR:10
DEX:14
CON:16 (+1 at 4th)
INT:10
WIS:8
CHA:19 (+1 at 8th (the +1 at 12th will go here))
Trait: Tattooed Mystic (Human)
Trait: Overwhelming Beauty
1: Feats: Noble Scion (war), Skill focus knowledge Eng. MT*: False Flanker
2: MT: Mesmeric Mirror
3: Feat: Divine Fighting Technique (WotSS**) TT: BS***: Psychic Inception
4: MT: Fearsome Guise
5: Feat: Eldritch heritage (Nanite)
6: MT: Spectral Smoke
7: Feat: Intense Pain BS: Lethality
8: MT: Mask Misery, Skill focus: Bluff
*: Mesmerst Trick
**: Way of the shooting star
***: Bold Stare
I didn't include items or spells because that should be up to you, but here are some things that'll work really well with this build and most mesmerists:
Ring of the Sublime - permanent remove fear
Mask of the mesmerist - buffs to core class features
Mesmerizing tattoo - turns your stare's -3 to -4
Weapon Enchantments: returning and cruel - So one of the things I love about this combo is adding in a pre-implanted fearsome guise: So pick your target, activate FG, throw the weapon. If it hits they are shaken and sickened and ready for a save or suck spell next round with a whooping -8 to their saves (-2 shaken, -2 sickened, -3 hypnotic stare, -1 Mesmerizing tattoo). If you have enough gold at this point for a +4 or if you don't see yourself ever throwing your weapon spell storing is great with some of the spells on your list namely bestow curse, turns the -8 into a -14 if you pick wisdom drain.
