Hidden Cities - 1
The Tundra is not a very hard stage. Bear in mind that the boss is the High Angel Mizal. You can recruit her sister, Yushis, in the stage Antalia. If you want, you can skip this stage, beat Antalia and recruit Yushis so she can be the one to put an end to her corrupted sister.
You start in Wilke's. Send a unit north along the road to Endis Ro, and then take the left branch of the road across the river. Once there, liberate the next city along the road, Kotz. The enemy should be coming to that point by now, but you've effectively cut them off.
Send a second unit west of the base along the road, liberating both cities and the Temple at the end, and then go into Herald C on the west shore. Head north across the ocean from there, liberating the island city of Mohnso, and cross again onto the mainland. Liberate the Temple on the western island, the city east of it (Intahi), and the city east of it (Ells Wah), the latter one being on the main road.
Now just send a flying scout around the map liberating everything you missed except for the two cities north of Ells Wah. Find all the treasure and liberate the hidden Temple in the southeast corner of the map. In Mohnso, you will obtain an Egg of Wonders, which will allow you to recruit a character anywhere, not just in a city. At Ruskayah, one of the cities along the western road, you can pick up a Flame Sword.
When you're done and when the flow of enemies ceases, send a unit north of Ells Wah into Balleny and north of that into the enemy base. If you recruited Yushis, use whatever unit she's in.
Yet another easy boss. Mizal gets one cast of Jihad, the most powerful White spell in the game, however if you send a nice, high-ALI unit after her she won't be a problem. If you have any of the Sky Knights, use those as they have high ALI. The Ice Giants are nothing to worry about because they miss often. A Magician card will severely damage them, but you could just put two or three spellcasters in the back row (like the Cherubim and Mage in the illustration) and with the Leader tactic, they'll kill Mizal quickly.