Hello, I'm a complete novice at modding TS3 and I wanted to see if someone can tell me if a) my idea is actually possible to implement and b) if there's any tutorials or tips you might have for me.

What I want is to create a poison mod. I've thought up several ways to do it (a custom elixir, chemistry, a recipe...) but so far I think the best option might be as a harvestable cooking ingredient.

Browsing around the forums I found tutorials on how to make a custom plant with CCLoader, and I've even found a mod that allows the ingredient effects to be applied to cooked foods.

What I wonder now is how exactly I could add the death effect to the ingredient. I imagine this could be done by adding a deadly moodlet whenever the sims eats the food, or maybe just as an effect (like how apoles affect pregnancy). I guess this is related to script mods, but since I am not sure, I figured I'd just ask. Thanks!

This would likely require a fair bit of script modding (most things do, as far as adding new functionality goes) but I do think it's possible.
My number one recommendation in that regard is that it's a lot less disorienting to follow tutorials if you're already past the 'I don't know what I don't know' stage when you start. By that I mean, if you familiarise yourself with the tools and skills required outside of a TS3 context first it's a lot easier than trying to do something for the first time and do it the incredibly specific way a game from 2009 requires you to do it in.
Looking into some regular C# tutorials will do you good.

Then it's onto the 'Getting Started' portion here to get the game files you need, then skip to this one as it's more up to date and accessible.
Here's a link to Nona's moodlet tutorial, also.

The best bet will probably be to look into some of the existing moodlets that trigger death on expiration (ie. starving) or how existing mods with fatal interactions directly trigger a death type. The jellybeans from Supernatural also come to mind, if you were to make a variant of that script without any of the other possible effects except dying.

There are a few script modders around here who may be able to help with specifics, it's just a matter of when they're around on the forum

I'll take a look at it! Thanks!

This just came up in another forum, not too long ago, and seems relevent. https://modthesims.info/d/493140/mo...s-for-pets.html This mod has a "ghost" potion, that apparently kills the sim. Looks like a good place to start. I do not know what is involved, and it is not something I would know how to do, but you might be able to look inside this mod and find what you need.