Would making a video game be considered "business in intoxicants" or "business in poisons"?

Maybe it's more like entertainment: analogous to being an actor or a musician; or telling stories or making pictures.

There are vinaya rules about what constitutes killing: a condition is that there must be "intention to kill". For example if you carelessly knock something off a cliff, which falls on someone underneath and kills them, doesn't count as "killing" because that's an accident, i.e. there's no intention to kill. I'd argue that similarly, when people play a video game there's no "intention to kill".

You could instead argue that playing is intoxicating; but I think there's a more direct analogy, i.e. it's like playing a game. I think there's a sutta which warns that too much game-playing (especially with disreputable companions, perhaps gambling, perhaps spending too much time at it, perhaps becoming 'addicted' to the activity) isn't profitable for a lay-person.

Another direct description of the activity is that it's pursuing sense-impressions: so maybe it's samsaric. I think it's more like the seventh of the eight precepts:

7. I undertake to abstain from singing, dancing, playing music, attending entertainment performances, wearing perfume, and using cosmetics and garlands (decorative accessories).

It's not the first ("killing") nor the fifth ("intoxicating drinks and drugs, which lead to carelessness").

You could perhaps, possibly, argue that it's the fourth:

4. I undertake to abstain from wrong speech: telling lies, deceiving others, manipulating others, using hurtful words.

Intoxicants here, I would think of as intoxicating chemical substances such as alcohol and drugs. When drunk or high with these, they may impair your ability to discern between right and wrong, beyond your conscious control.

I'm not sure if nicotine can be considered an intoxicant, as it can be addictive but it does not impair judgment.

Games can be addictive but it certainly does not impair one's judgment. It does not make you drunk or high, beyond your conscious control.

Some might argue that a romantic relationship might make you more drunk or high than games, but that too does not impair your judgment beyond your conscious control.

I'm trying to make a point here that games and entertainment should not be considered "intoxicants" in the context of Right Livelihood and the five professions that are unwholesome. But there is a question on whether actors may go to hell, which discusses the ethics of entertainment. You might find that more relevant to your situation.

In my opinion, games with weapons do not injure anyone, so this would not violate Right Livelihood in the context of the five unwholesome professions. However, this too is subject to the ethical problem of the "actors may go to hell" question.

While I don't believe Buddha's advice here is merely pointed at the physical domain, or a matter of income, it is helpful to look beyond Right Livelihood and at all elements of the Noble Eightfold Path together. Consider the impact of Wisdom (Right View, Right Intention), which, while being a different nature, can still relate strongly to Ethical conduct.

Your questions seem to be more concerned about how real videogames are within Buddha's principles. I don't suggest being light with it as though it is "harmless fun," when in most cases, games are created for a certain kinds of indulgence and gain - their purpose for entertainment. A video game is arguably not much of a physical matter, but overall, it is indeed an astral matter that is capable of absorbing energy from most people (and even forming addictions).

Thus it is not just entertainment, but consider what emotional energy is being entertained. Is it hate? Anger? Pride? Popular games may take on such a quality, but not all games or companies are aligned with this. For example, thatgamecompany has created positive gameplay, with games noted by many as beautiful.

The Videogame industry/market includes both its businesses and its consumers. Whether or not you are producing and selling a game as an form of business, consider that you are also accountable for playing them.

Although I would personally avoid playing such games (involving weapons, killing, etc.), there is great and simple wisdom in The Middle Way, which may suggest that if you play such games ('objects') occasionally, non-attached, perhaps the impact is insignificant, or less significant. When disinterested though, such games lose their appeal anyway, which may contrast with games that are naturally uplifting. For many other reasons, I am unconvinced that playing games is a trivial matter when devoting oneself to a spiritual/religious path.

Following the aforementioned link provided by ruben2020, there is a link to the Talaputa Sutta. A comparison can be made here with Buddha's words on actors, which show how the actor may become an agent - to the extent of becoming "intoxicated and heedless, having made others intoxicated and heedless". This illustrates laws between the being watching and the thing (or actor, game) that is entertaining:

Any beings who are not devoid of passion to begin with, who are bound by the bond of passion, focus with even more passion on things inspiring passion presented by an actor on stage in the midst of a festival. Any beings who are not devoid of aversion to begin with, who are bound by the bond of aversion, focus with even more aversion on things inspiring aversion presented by an actor on stage in the midst of a festival. Any beings who are not devoid of delusion to begin with, who are bound by the bond of delusion, focus with even more delusion on things inspiring delusion presented by an actor on stage in the midst of a festival. Thus the actor — himself intoxicated & heedless, having made others intoxicated & heedless — with the breakup of the body, after death, is reborn in what is called the hell of laughter.

Entertainment itself is for the mind as a form of escape, it is simple enough to ask yourself if Buddha would advise for you to continue what you are doing, due to the level of intentions and mindset are you ascribing to it.

Depends on what game one's making. There're games designed to boost memory and prevent Alzheimer's disease, or math games to help kids learn math, or various educational games to make learning more fun and interesting. On the other hand, there're games with sexual contents or violent contents which only increase one's defilements. There must be some bad kamma if one's involved in creating games for kids to enjoy blowing people's brains out or ripping their heads off (like Mortal Kombat and other fighting games)..

Creating a video game doesn't fall into any of the 5 specific wrong livelihoods for lay people. A video game does allow people to escape from reality but so do fiction books, music, delicious food, beautiful scenery, daydreams and countless other things. Our world is filled with things that can be "intoxicating" if we choose not to guard our sense gates.

But a more straightforward concern might be that playing video games can create negative karma for the player because of the competitive "win at all costs" mind state you need to be in to play most games well. You can get blood thirsty due to the excitement of competition and greed for loot and status within the game can be overwhelming. And it seems unlikely a game developer would not play games along with developing them. :)

So though it may not be one of the 5 specific wrong livelihoods for lay people, it certainly comes with some karmic concerns.

I'm of the view that if the question, "is this wrong?", is worth asking, then it is wrong, at least for you. Your conscience has spoken.

If my shoe hurts my feet, I don't continue to wear it merely because it's a brand name shoe that others wear without consequence. If my feet hurt, that should be enough. Of course I can still become a fashion victim and continue to wear it because it's cool or because I paid too much for it.

Similarly, people often stay in careers they know is wrong for them because they've invested too many years in it, they are good at it or because they like the money or prestige or something else.

Inner peace comes from listening to what goes on inside and reacting appropriately.

You seem to think games are addictive, which they are designed to be of course, and I recall studies have showed this objectively, especially in teen populations.

VC success metrics for game companies include statistics like duration of uninterrupted play for their titles. Comments by top gamers on steam, show they've logged thousands of hours on a game. I recall one comment went like this, 'my girlfriend has left me, I've lost my job, my friends don't speak to me anymore, but I can't stop playing and I love it'. It's almost like Vegas. Sadly, this outcome is not unusual for really hard core players.

Yet, interviews with competition players, who stand to win millions of dollars in matches always indicate that these players somehow have mastered emotional independence from the outcome of the game, and this is what makes them better at matches.

I think you have to respect your feelings rather than try to measure it across some universal standard.

Edit: I want to add, please be smart about this. Most people can't quit big parts of their life, like a career straight away, but eventually over several years they can taper it down to the point where they can quit. The idea isn't to become homeless. I say this as someone who's quit his job to focus on a richer spiritual life.