Marignon is a nation inspired by crusade-era Christianity and in the Middle Age it's a nation of fire and astral magic backed up by heavy troops and crossbows.
Mages: They have strong recruit-anywhere priest-mage Inquisitors that can be good for controlling enemy dominion within friendly territory or just accompanying armies with some good holy and fire magic. Witch Hunters bring some astral along to give some possibility for communions or reverse communions. Their capital-only Grand Masters are powerful fire/astral mages with some air and earth access, all on top of being sacred for decreased upkeep. Initiates are a little confusing since they're just basic fire-1 mages, although I guess they'd be good One thing to note about fire mages in general is that fire magic reduces the old age threshold and the general number of magic paths increases current age, which means your fire mages, especially the powerful ones, will probably all be very Old. This might not matter for the most part, but they won't be particularly accurate with their spells and they tend to accumulate afflictions as the game goes on, which can be a problem.
Other Commanders: They have an interesting array of stealth commanders in that they have Scouts, Spies, AND Assassins so they can create unrest with Spies or try some assassinations if they want. They have stealthy holy-1 priests, which I guess could be useful for stealth preaching in enemy territory if you add in something like a Stone Idol. The main problem with non-mage commanders is that every turn you recruit one is a turn you're not recruiting a mage. As far leading armies, they'll probably just use their mages since fire magic makes them particularly potent leaders.
Troops: Marignon's troops are pretty much entirely heavy infantry with a few knights. Their Swordsmen, Halberdiers, and Pikeneers cost a pretty big chunk of resources, but that just means they're pretty standard as far as heavy infantry go. Their downside? No shields, so they're vulnerable to archers and crossbowmen. Men at Arms are similar but they trade their big weapons for a standard sword and shield, making them better arrow-catchers.
The Royal Guards are their recruit-anywhere knights. They're decent. Their defense is high (pretty standard for cavalry) and their protection's fairly good, but they don't have lances, so they don't get any charge bonuses for their first attack. They're still good for flanking and are probably worth using in little groups, although they're pretty expensive so it'll be hard to scale up much.
Marignon has some interesting options for sacred troops. Flagellents are generally just thought of as bad. They're cheap and have really good morale and flails (good against heavy armor and shields), but other than that they're just bad. They have no armor or shield so they die in droves to ranged attacks, plus you can't use earth blesses to boost their protection since it boosts existing armor, which doesn't exist here. On top of that they have a 75% chance to start afflicted, which just drops their usefulness even more. These guys make me really sad because I really want them to work, but it just takes too much.
Knights of the Chalice are better. They're pretty expensive for standard troops, but they have high protection, they're quick, and they have lances. Adding an earth bless will skyrocket their protection and most other blesses would probably be equally beneficial (water would make them seriously tanky, astral would boost their magic resist to respectable levels, fire would help their damage output). A bless would be a worthwhile strategy for Marignon based on the combination of the Knights of the Chalice and the fact that nearly all of their mages are also sacred.
Other: I'm going to put things like national spells and dominion effects here. For Marignon the focus is on their national spells. They get some pretty nice angel summons, including Contact Harbinger which will boost them most of the way into air magic (they get A3, but you need A4 to forge boosters). They're all pretty good candidates for thugs and maybe supercombatants (especially the Seraph), plus they're sacred so they'll benefit from blesses as well. Holy Pyre is useful as a combat spell that doesn't require research and is a good alternative to Fireball since it has lower damage but a much larger area of effect.
Base Strategy: Welp. It's the first nation I picked and it turns out it doesn't have publically available actual strategy guides. I found some random odds and ends though (the best one's
here) so here we go! For initial expansion you could probably just build random units and end up coming out ahead. Heavy infantry, knights and crossbows are all good against indy armies. What you'll probably want to do is a knight/crossbow combo since that will scale well into midgame when you start adding things like Flaming Arrows and Wind Guide. Fire evocations will be seriously useful, and Phoenix Power can be used to boost your fire magic. Lightless Lanterns are good for boosting research. Summoning things like Fire Snakes or Summer Lions can be useful to act as a screen for your fire mages since the enemy will get tied up on your fire immune troops while you rain fire on their heads. Mid-game you'll probably want groups of angel thugs flying around wreaking havoc. Angels of Fury have fear AND blood vengeance, which makes them good, especially in groups of 3 or so. Gem generators are something I'm not used to playing with since they're heavily restricted in CBM, but you'll want clams. You'll want lots of clams. I've seen things about fever fetishes being useful although you'll probably want them on random indy commanders because it automatically diseases whoever has it equipped. I'm going to leave late game for all nations to other people because I have literally zero experience with end game vanilla Dominions 3. Off the top of my head, Marignon is better equipped for Wish than Tartarians, although getting into death isn't particularly hard.
Pretender Ideas: I'll brainstorm a little bit for pretender designs for each of the nations since this is the part of Dominions 3 I like the most. First and foremost: Marignon needs resources. Production 3 is worthwhile. If you're making a lot of knights you might want gold, but for the most part Marignon isn't super expensive. Growth could be worthwhile because I think it helps prevent afflictions caused by old age. I wouldn't be a huge fan of a bless strategy with Marignon, although it's certainly not a terrible idea. The main reason is that Knights of the Chalice are capital-only resource-expensive recruits, so it's hard to get a large number of them. Minor blesses are certainly useful, though, especially an earth bless for the reinvigoration your mages will get. Marignon doesn't have a huge need for an awake pretender, so I'd say going with decent Production 3 scales with a minor earth bless and high astral magic (with maybe a splash of death or nature) on a sleeping or maybe even imprisoned pretender might be the way I'd go.
