Madness
If all you care about is save penalties, it's hard to find anything better than the Madness domain's Vision of Madness. No save, just a touch attack, and your enemies take a penalty of half your level, not only on saves, but on attack rolls too, for a full 3 rounds. It will boost skill checks by an equal amount, but surely that'll never come back to bite you.
Options for getting a domain as an Arcanist are rarer than I assumed they'd be, but the Emissary archetype (you have a familiar, right?) gives you a single use per day on your familiar, and a few other goodies. If what you want is not to affect every enemy with every spell, but a very targeted, once-per-day guaranteed hit, an Emissary can easily give an ancient dragon a -5 against your spells without even using your action.
Misfortune
In the same way, if all you care about is save penalties, the Misfortune hex is very strong for an at-will ability, giving roughly a -5 penalty to all relevant rolls for a round, extendable for 6000 gp and a move action. Or, if you want a no-save version, there's the far weaker Evil Eye hex, with a mere -2 penalty to saves. On a failed save it lasts for the rest of the fight, but even on a successful save it lasts for a round, allowing you to Cackle it. However, there's no Witch Hex arcanist exploit, and Extra Hex requires you to already have hexes.
Luckily, the Stargazer prestige class is light on requirements and heavy on a mishmash of star-themed powers: for just one level (not even reducing spellcasting!) you can gain the Misfortune or Evil Eye hex. The problem is, your save DC will be wretched, with an effective witch level of 1. Evil Eye is still decent, though, and three levels of Stargazer provides a familiar (Emissary?), +2 on initiative, a hex, at-will Overland Flight and Lesser Planar Ally with conditions, and more! Moreover, you can take Ritual Hex for a flexible hex - Cauldron for Brew Potion? Healing for Cure Light Wounds at will?
Majesty
While Intimidate is not an automatic success, it's still your best bet to make your enemies cower before you. Unless they're immune to fear (not uncommon), Intimidation is a roll against a flat* DC, and no matter your opponent's will save bonus it will still inflict Shaken if you succeed. Various options boost Intimidate, especially traits and some spells, but you really only care about one ability: swift action intimidate. I'm sure there are more ways to get it, but the main ones I've found are a trait - once per day, for killing that one big enemy - and a feat - which gives tremendous benefits for tremendous investment, with stacking fear and at-will swift action intimidate.
*10+hit dice+wisdom modifier isn't quite a flat DC, okay.
Monkeys!
Okay, so Mad Monkeys nauseates, not sickens. I had to keep the title theme going, okay? But if you want a terrifyingly powerful low-level sicken, Summon Monster+ gives you... two skunks. No-save, automatically sicken for 1d4 rounds, 1-3 skunks. Wait, this is a high-level effective version because it sickens with no save on a touch attack? You could sicken the aforementioned ancient dragon with a skunk. Who knew? Best of all, you can Quicken this pretty easily as it's a level 1 spell. This might be worth taking Versatile Summoned Monster for just to get flying/burrowing skunks, I don't know. Or maybe craft some poppets with flight and extra health to carry your skunks around, I don't know.
