For some reason it's not even on the wiki. It's not expensive to make, though, IIRC. I think it's a one-ingredient mixture, probably Slimy Fluids. Lightning Jam and Anti-Dark coating are expensive ones in terms of ingredients. It does require getting the Workshop upgraded to level 8, but that's not too extreme. Beyond that, you don't need that many of them, you're just using them in Mount Firestorm. They can be helpful against some enemies in the Clockwork Forest, too. You can probably just use the one you pick up plus buying the Alchemist's initial stock of them.
Nah, I just checked in game. It's a 2 ingredient coating. One is Ether, which is whatever, though it needs 3 pieces of it... which... ouch... The other is Jelly Jam... which, ugh... bigger ouch given that this one's pretty rare, the best repeatable M.Atack booster in the game, and also needed for Lightning Jam coating. It's also 470 gold at base price, making it the priciest weapon type coating in the game. Poison is 420 and Nasty Oil is 120. That said, it's obviously still cheap compared to the Anti-Dark Coating... though that's not surprising considering how stupid useful that particular coating is...
As for the wiki... The wiki doesn't mention a LOT of things. It doesn't even have a proper entry for the Clockwork Forest quest.
Also, the less said about the walkthroughs, the better. They're horribly outdated and trying to follow them identically will not work because of changed HP costs for stuff like harvesting and all sorts of other balance changes. Still useful for navigation purposes for the most part though. At least when it comes to most of the Demon Generals.
SO I have played a bit into the game
I not finding any options to push Aura to do shady stuff, or evil/shrew aligned actions (even if unintentionally) . Especially since I tried to keep her corruption high. Are there any options like this, or do I have to wait later in the game with more mind upgrades ?.
I just like corruption where she starts doing evil stuff thinking its for justice. You know that twisted Justice trope? Twisted is great affinity with corruption :3
You don't have much of that early on. But later, you have lewd and not so lewd choices involving twisted things that Aura can do to further her goals "because it's ok as long as it helps kill the Demon King" or the like.
How much that falls under what you're looking for, I can't say. You might enjoy a particular late game quest called "Justice of Pride".
That said, yes, you do need to get deeper into the mental changes for that to be available. In particular, you need to unlock Vice, which is a corruption stat that allows Aura to do stuff like steal, or throw people under the bus so to speak "for the greater good" and other such things.