Note: This was authored by an anon who added it as a strategic overview. Since it was not that, I moved it here.
Marignon is a classic heavy infantry nation, levying expensive but powerful and well-protected men dressed in fancy clothes. This, paired with excellent Fire magic, means that it is both powerful and straightforward. To round out her magic paths Marignon has good Astral as well as modest Earth and Air access off the bat. She also has excellent priests in the form of F1/H2 Inquisitor and H1 stealthy Friar- both of whom can lead armies. Arriving late but perhaps stealing the show nonetheless is the Harbinger, a national summon in the form of a A3/H2 priest/mage with amazing stats, Flying, and Invulnerability.
Your main strategy will likely be to form a line of Swordsmen to block the enemy while your ranged damage dealers wipe them out. These will likely be Fireball spam from your Witch Hunters and Wind Guide/Flaming Arrows Crossbowmen. You can supplement this with brave lance charges from the dashing Knights of the Chalice and Harbingers raining lightning bolts, tooting their horns, or (most likely) as thugs wreaking havoc in the enemy's rear. If you're feeling particularly bold you can summon some of the higher-tier angels, but the cost/benefit on those isn't as great as it is with the Harbingers.
If you're facing lots of enemy archers, you might want to tell your X-bows to shoot the archers and your infantrymen to just perform a gallant charge instead. You'll lose guys but it's better than hanging back and watching your them get torn apart without being able to respond.
Your sacreds are the crippled and weak but cheap and recruit-anywhere Flagellants and the amazing but incredibly expensive Knights of the Chalice. Flagellants make great suicide squads and even better anti-archer chaff with a major Blood blessing (and perhaps a minor Fire) but are gimmicky to say the least. With the right blessing, Knights could make an effective elite strike force later in the game when you no longer need your capital to pump Pikes, Swords and Crossbows, but they probably won't be a game-changer. As such, your bless can be safely considered to be secondary to scales and magic diversity when designing your pretender.
Weaknesses include a complete lack of Water, Death, Nature, and Blood magic as well as pitiful Earth access. A pretender who could get into some of those paths would benefit Marignon greatly. Fire resistance can be troublesome to deal with as well, but can be overcome with Astral magic as well as good old fashioned steel. While relatively cheap gold-wise, Marignon's units require a fair bit of resources and pumping out enough each turn to survive is something which must be planned for.
Also, the ones you'll want to recruit don't have shields! I mean what could be going through their heads? "Yah brah don't worry, our, like, faaaith will protect our asses from those arrows brah! 'sall good, fam!". Yeah. Cast Arrow Fend, or prepare to lose some dudes to enemy archers. There's not much you can do about it early on though and tribal indies will be a pain.