I think the benefits of a summoner build are a. you're making good use of your high Presence, b. it's a good use of your encounter power; it means you're not generating much threat in the first round of combat and you have an effect that usually lasts the whole fight, and c. towards the current end of content (which admittedly is annoyingly late) the pool of available summons becomes much bigger and more diverse, letting you pull different tricks out of your bag.
I am very much a the-best-defence-is-a-good-offence player; so I focus on damage rather than status moves.
STATS
So high Temptation is important for the effectiveness of your charms, and Leadership will boost the stats of your summons and allies so also very important. Leadership is tied to Presence, which is great, but Temptation is tied to Strength, which is not, so boosting it with equipment and alcohol carries you. Obviously Sexiness is super-important but this takes care of itself more readily than the other two.
I maximise Presence, Cunning and Agility. Leadership and Sexiness are both tied to Presence. Cunning boosts your crit chance, and Agility your evasiveness. I used to put a few points into Willpower but that's become less important since charms and spells were split out, though options for non-tease-damage charms are still pretty bad, so you might want to boost Willpower/Spellpower a little. When possible I'll drink a strength-boosting alcohol before a dungeon because you will feel the benefit of all that extra Temptation (and/or Spell Penetration).
ALLIES
I love Azzy but she is cursed for charmers, since her sleep 'buff' converts any tease damage you do to pheromone damage, which 9 times out of 10 is less effective. Many bosses weak to tease have high resistances to pheromone. Otherwise I rotate allies pretty freely, though I make sure I have a tank and usually a healer - I can act as a healer but at a cost of other options. I don't get much use out of Kiyoko, Viv or Agni however,
because they're terrible (maybe their party roles are too similar to mine?).
A strong tank is important. Quin's, Arona's, Brint's and Tui's tank sets are great. I haven't tried Ryn's new Glacial Guard set, but it also looks promising. Azzy's default set is good for roaming around but I don't trust her for dungeons or bosses, as noted above. I'll compromise with Arona's holy damage set, since with it your party will be vaporising anything corrupted.
Cait and Tui make good healers, and Azzy does when her 'buff' isn't being a hinderance. Ryn probably would too, but I like her default set too much, even though Harrick is eternally a third wheel. Ryn and Tui make a strong team. Any ally who can cast 'Blessing' is, well, a blessing.
POWERS
At level 7 my power choices are:
At Will
Bolstering Dance - Always my first choice all game. It's a great healing ability for keeping the party topped up and minimising the amount of actions your party has to spend healing. Strong enough to stay relevant all game.
Great Heal - This spell is so powerful that it's fantastic even if your willpower is low. Soothing Dance is awful by comparison. Generally if I don't have a healer in the party - say because I took Ryn and Arona to Dracia, or, for some inexplicable reason, I have Kiyoko in my party - I'll switch in Great Heal so I can be the main healer, but I'll miss Bolstering Dance.
Recharge
I'll have one single-target and one multi-target recharge power - usually this will be Suggestive Sway and Dischord, but if I know I'm approaching an enemy with high tease resistance (elementals and other people's summons are the worst) or weakness (anything with high corruption), I might switch things up.
Single
Suggestive Sway - Make three tease attacks against a single target. With high cunning, good chance of one or more crits. Against a single target with low tease resistance, this can nearly one-shot many fights. I used it against the Lureling and dealt over 1000 damage in a single action.
??? - A non-tease attack is a lot trickier now, as charms don't give you many options. There are a couple that deal mental damage, but enemies resistant to tease are often resistant to this as well. Celestial Frost and White Fire are surprisingly effective even with low Willpower; there are probably other spells worth exploring, especially if you've boosted your Willpower.
Multi
Dischord - Fantastic, powerful, multi-target attack. Not much more to say; consistently reliable.
Allure - not the most powerful, but if you know your enemies will be weak to tease, a solid choice.
Encounter
A variety of summons. Kiyoko is great early on. The Fire Dancer is a solid choice once Kiyoko is freed. Later in Act 2 you unlock a whole range more to explore. Phyria is baaaaaaaad, but Cassidy is a solid choice for Undermountain where common roaming elementals resist tease and fire, and tons of options open up to play with once you progress through Khor'Minos.
Ultimate
Inspiration is good in a pinch. There are other solid choices depending on how you feel.
GEAR
- The Aphrodisiac Whip has the best stat boosts for a Charmer - both sexiness and temptation. Ashe's stats aren't as good but her damage type gives you more versatility and, you know, it's nice to have another friend along.
- The Parasol, purchasable from Kohaku, boosts Leadership and Temptation; this is my favourite offhand choice. The Rosebloom Shield is a trap for the same reason Azyrran is.
- The Helm of Heroes gives a tasty boost to Leadership and its Heavy tag doesn't affect that one trait affected by heavy gear because only your body slot counts. It isn't a great vibe visibly, so let's imagine the game, like all good RPGs, has a 'hide headwear' option.
- Choker of the Pain Slut boosts temptation and lowers incoming crit damage a bit. You can stock up on Ice Wine from Kohaku to keep your libido under control.
- The Cloak of Winter is, I think, the only cloak that boosts sexiness.
- Royal Leathers and the Kunoichi Bodysuit are strong choices, and there are arguments for a few other light armours.
- Underwear that boosts Temptation rather than Sexiness should give you more mileage.
- For your waist slot, Fluffy Sash probably your best bet for stats, or the Senninbari if you're
a coward cautious.
- While it's not tied to Sexiness, the Golden Carrot's crit-boosting will never not be welcome.
- Various good foot options but I settled on the Kunoichi Footwear.
- For rings, the Ring of Temptation boosts Sexiness and (predictably) Temptation. The Guldring boosts Leadership considerably, though I haven't gotten far enough in my current playthough to test if its special power works on charms as well as spells. Hana's White Blossom Ring gives nice crit boosts, despite the fact that, annoyingly, it's tied to Willpower (grrrr...). Sleeping while wearing the completed Ring of Fate unlocks a strong summon power that you don't need to be wearing the ring to use.