Bad North

There are a few things you will want to keep in mind for this achievement.

1. Note that you can turn on level restarts. Restarting levels if something goes awry, or your setup does not work, will not incur any kind of penalty.

2. I would strongly recommend equipping one of your starting commanders with the Philosopher's Stone and prioritizing fully upgrading it. While this incurs something of a penalty in terms of troop strength in the first few levels, it definitely pays off in the long run.

3. I find that most abilities, as well as a handful of the items, underperform. I would recommend prioritizing upgrading your units rather than their abilities and items, with the exception being the Philosopher's Stone and the Ring of Command, which constitutes a direct upgrade of that specific commander (I recommend using it on Spearmen. The additional manpower will provide that commander with more utility than your average Spearmen, and thus allow it to be positioned more aggressively). Mines have their uses, but they can be dangerous if used irresponsibly.

4. Archers are remarkably powerful when used to clear out enemy ships before they reach land. Whenever possible, you should position your Archers as aggressively as you can, so that they can take enemies out of the equation before they have a chance to disembark. Any enemy that doesn't set foot on your island is an enemy that won't have the opportunity to weaken your melee units. But make sure to always be ready to move them out of the way and into cover, so that they aren't your first wave of defense when the enemy comes ashore. And be wary of ranged units.

5. In the final level, keep in mind that your only priority is to keep your commanders alive. I found that using a combination of Spearmen (enhanced by the Ring of Command), Swordsmen and two sets of Bowmen in order to turtle on top of a hill with a building on top, and only one point of access, allowed me to basically lean back and watch, as the game beat itself. Make sure that your Spearmen are positioned so that they are the first thing the enemy has to deal with as they climb the narrow path. Position your Swordmen next to them, at the top of the path, so that any units breaking through won't overrun your Spearmen or your Archers. Your Archers will automatically thin out the horde of incoming enemies. Your Swordmen can be sent out to pick off any straggling ranged units as necessary, or to quickly deal with Brute Archers, which constitute the only real threat you will have to deal with, as they can rapidly pick off a commander if you're not paying attention.

That's all there is to it. If you are struggling keep these hints in mind, and hopefully you won't be overrun by the Viking Horde.