I’m thinking of making an illusionist for an upcoming gestalt game. What classes do you think would make a good combination for a gestalt illusionist? Is mesmerist a good illusionist?
Mesmerist is really more intended to be for enchanters: however, most illusion effects target Will saves which are helped by hypnotic stare. Keep in mind that the mesmerist is Charisma based, and a wizard (I infer by illusionist you mean illusion-specialized wizard) is Intelligence based, so you may have issue there.
Be an illusionist and... a fighter! Nobody will expect the brawny fighter to be a secret spellcaster. And don't forget to take those fiddly feats to disguise your spellcasting.
Usually when making Gestalt I am more focused on shoring up weaknesses then maximizing 'on thing'
Brawler, Ranger and Gunslinger are full bab, d10 and have good fort and ref saves, which would give you all good saves. Their particular class abilities won't add a whole lot, but should provide some flexibility. I'd probably lean to Brawler of these, since being unarmed and illusion magic seems like at times it could work out well, and if we are looking for flexibility anyway, nothing is more flexible than brawler. If the point buy is low (or bad rolls if that is what you are doing) gunslinger might edge it out, since guns are going to be guns anyway and you don't really need much in stats to have them be effective backup options. Ranger's big attraction would probably be the animal companion, even a level-3 AC makes a good mount if you aren't planning on engaging in direct combat and the extra mobility is always nice.
Alchemist also gives you good saves, and uses your primary stat. While there isn't any direct synergy, it would give you a great deal of options for times when illusions aren't going to cut it.
Of the psychic classes (which I don't know all that well) occultist seems like the best fit. Uses your primary casting stat, gives you a good fort save (leaving only ref as weak, the least important in my opinion) and gives you 3/4 bab and d8 hd. You can work with illusion implements to continue the theme, or branch out to other schools.
Kineticist probably also deserves a mention, since it would give you all good saves and CON will probably be you second highest stat anyway.
I don’t mean the illusionist archetype but combat style. I want to use illusion type magic to control the battlefield. I don’t want to deal any damage myself.
I play gestalt a lot, but this style of character is somewhat outside of my wheelhouse. I played one once that was a bard, but that campaign didn’t last long. For this character I would rather boost their primary activity than make them more versatile.
Stats are high. A 17 and 18 nothing under 10.
I never really played an illusionist and you will probably lose quite some of the benefits of gestalt characters if you want to fully focus on illusion but possible class combinations I could think of would be Puppetmaster magus+ School savant Arcanist or wizard, with high charisma and high intelligence.
This gives you 2 class features that boost your spell Dcs, some swift action spells, access to the bard, wizard and magus spell lists, a huge number of spells per day and 2 ways to maintain your illusion spells without concentrating.
If you are worried about affecting undead with your mind-effecting spells, you could also take levels of dirge bard+ Sorcerer.
There really aren’t that many classes that boost illusions so you will probably end up with a lot of overlapping class features.
The Psychic class with the Pageantry discipline has an ability that allows you to concentrate on ongoing spells as a swift action, which is exceedingly useful with illusion spells. However, the catch is that the Psychic doesn't actually receive the best illusion spells in the game, the Shadow Conjuration spell line. However, since you're a gestalt character you can fix this easily by mixing your Psychic with either Wizard (probably illusionist) or Sorcerer (probably sage). While it does leave you a very defensively vulnerable (d6 hit dice and only one good save is atrociously bad by gestalt standard), it will give you the ultimate selection of illusion options.