I have faint memory of Asylum from some play years ago... maybe it was one time mission expanded into arc later?
Can you please elaborate on Ghosts? Can it be started immediately, and is there some unusal risk (cost)?
Yes, the arc was expanded some years back, and it starts from the asylum mission.
Ghost arc can be started after you get cover: scientists and parapsychology i.e. Promo II timeframe. There is some randomness to when the first mission appears. It is advisable to start the first mission early. The asylum mission can be accomplished already with helicopter, but for training purposes it's better to wait for getting the whole squad there with osprey.
There is no unusual risk with the ghost arc, as long as you are careful with which missions you get to. Some of them can be rather dangerous if you are not adequately prepared and don't know what they are. As I said, it's best to start with "haunted farms" and work up from there.
This is Important...does it mean that if you miss that mission, you can never progress arc? Are there are missions like that in any plot? I will definitely add such info to the list.
Regarding David Vincent mission. This is one-time entirely optional mission. It does give two chances of easy research into advanced alien tech, in addition to MIB loot.
There are many one-time optional missions in XCF in many plots. None of them are critical, but most of them provide at least something useful. Usually a chance at get some useful research by interrogation and a weapon.
The other ones are the following. I've listed them in the rough order of the most important to least important:
- Ambushing alien abductors w/ Gertrud Ellison (the most useful mission, allows you to capture live sectoid navigator, engineer and leader, which gives you access to early alien tech and psionics; you will need to know how to deal with this to get them alive; this can really boost your game if you get you know how to deal with this and get this in late Promo II or Promo III timeframe)
- Dr. Alpha's hideout (extremely useful and IMHO the second most important one-time mission: interrogating Dr. Alpha can you early access to psionics, which can be really useful if you missed capturing sectoid leader in Gertrud Ellison mission or haven't gotten the mission yet)
- Lo Wo's refuge (Black Lotus; you get ancient katana, which is excellent weapon, especially when used in Dreamscape missions)
- Meridian hunting (some research, capture or repurposing seeker drones may be also worth something)
- Natasha Morozova's hideout (Red Dawn; you get special VSS weapon which is great, and the best undercover weapon)
- Hell cruise with Dr. Hadriex (you get hadriex gun, which is now effectively superseded by better ghost arc weapons)
- Agent Wilheard's voyage (nothing too fancy at the point this appears)
- Horrors of antarctica (doesn't really give you anything)
- Project Samael (Cult of Apocalypse arc endgame option, doesn't really give anything useful)
As should be obvious from above the first one (and maybe also the next two) are very important missions. Whether or not you get them and deal with them properly will significantly affect your pacing and game experience.
I may have omitted a few that in practice occur only once but are not strictly defined so with "maxRuns: 1". There are also a number of more or less rare optional missions that can occur multiple times.
Regarding syndicate stages:
Can you please clarify relationship between branches/stages? Can you finish A without doing B (in case there is some finish), but mainly can you reach C without doing B...etc?
It's advisable to get Osiron as early as possible (no real downside) and unlock syndicate as early as possible.
The first branch of syndicate missions (syndicate warehouse, syndicate lab, syndicate monster lab) are rather easy and somewhat rewarding. You can also use this to terminate the monster arc (after abandoned syndicate lab), but usually you don't want to, at least immediately, because monster missions provide good training opportunities for you.
You just have to be careful with syndicate data seizure mission. Just skip it or at least don't successfully complete it until you're ready. If you do, this will trigger syndicate retaliation and three special missions with 8-16 hour timers (you'll need a fast craft to get into those). The retaliation will continue every month as long as you've completed all three.
After you've repulsed the syndicate, you will additionally get syndicate regional headquarters mission. By capturing the CEO, you gain Helix Knight improvement and unlock syndicate HQ mission (monthly chance to go there).
Depending on the stage of progress you may need to defer syndicate HQ mission for a bit, because it can be really difficult if a) you get bad spawn in the middle of map and b) you don't have good psionics. As said, Syndicate HQ mission gives you eventually by far the best transformation in the game (spartanism), so it's really advisable to complete the arc.
Mhm strange. Dagon was a laughing stock to me at Veteran difficulty, used them to get Promo III. I guess it depends how their role fits your playstyle, or I just got lucky. Anyway I removed cult ranking from the list - game is very transparent about cult differences and it is subjective.
The biggest challenge in Dagon HQ mission are gillman terrorists, which will fry your agents if any enemy unit spots your troops. Obviously savescumming may help there, but I'm speaking from ironman-type experience. If you want to reduce the likelihood of losses, you may want to have plastic-aqua armor before you go there, which gives some decent protection against ELECTRIC (usually you survive at least one gillman hit) and makes you immune to CHOKE (so you can spam gas grenades).