If you act fast, you can scrape together some levels, cash, and gear to prepare for the invasion.
At day 100, I managed to get Power Draw 8, a Whitewood Bow, Riding 6, a Geldarin Warhorse, and 20 quivers of arrows. I married Princess Linthradil, so I could put my army in a garrison and get it back later. This was important.
I started attacking Zann Advanced Scouting Parties. They have 60-90 cavalry, and the rest are infantry. There are no archers in this party. Mounted Kamikazes and Kamikaze Warriors do not use shields or throwing weapons. Some Black Warriors use throwing knives and shields, but that's a trivial concern, and they run out of them quickly.
You lure the party onto a large Plains map with as few obstacles as possible. You then ride around in circles shooting all of the Mounted Berserkers, with one bow and three quivers equipped at a time. Keep restocking - each Berserker should take 3-4 body shots to kill. Make sure you don't run into any obstacles or the map border, or you will most likely instantly die.
Once you kill the Berserkers, try riding around the infantry blob and shooting shots at max difficulty range only. Because there's so many of them, it's easy to score a hit, and each 12/14.4 shot difficulty hit that lands will give you huge amounts of Archery Proficiency.
Specifically because of the Zann's weakness to archery, and the abundance of otherwise powerful melee units and enemy archers in the mod that prevents me from powertraining my melee proficiencies efficiently, my proficiency spread looks like this;
Each time you win a fight alone against one of these parties, you will gain
- Tens of thousands of aurums from loot and any stragglers you knocked out with a Jousting Lance.
- 60-100+ Renown
- 40-60k personal experience.
- Huge amounts of shared experience for INT companions like Slyter and Alindel
You need to stack on weight FAST before Invasion Day, and this is one of the best ways to do it.
Default invasion day appears to be Day 157. If you can get your levels up fast enough - Strength to 30, Power Draw 10, and a Darkforest Ranger Bow, backed by a decent army of 100-200+ men - you'll be in position to single-handedly blow up entire Zann invasion columns in siege defence.
Learn the layouts of the castles you're defending. There are often ways to get into faraway positions where Zann archers won't shoot you, and if you're far enough to the side you'll be able to hit even enemies that have shields. Search for good shot angles, keep stealing arrows from your men with the O key wherever possible, pick up dropped arrows from dead friendly archers, and if all else fails consider killing teammates for their arrows so you can keep firing. It sounds brutal but it's worth it. You can probably score 20-30 kills with one quiver of arrows. For your allies to die for such a noble cause - it's an honour.
You'll level up so quickly from the sieges that your character will quickly become superhuman. The shared exp + Renown bonuses also help quite a bit especially later on.