Fire Emblem: Shadow Dragon/Chapter 13

"The Akaneian heroes hurried in Altea, but they would not go unchallenged. Waiting for them at Fort Menedy were Grust's artillery regiment, the dreaded "Wooden Cavalry." Missiles crashed down, rocking the earth as the enemy ballistae rumbled forward. Had Marth and the League any hope of triumphing over such firepower?"

Preparation
First of all, make sure you select Midia (Paladin) as one of your characters. She is necessary to recruit a character in this chapter.

Lena with a warp staff as usual

bring lots of cavaliers and if Caeda is a dragon knight, bring her to.

Begin
These are the main things to do here (in no particular order and some are described more in detail later):
 * Recruit Astram with Midia. (Make sure to cover all the flanks and keep her healed.)
 * Visit the village to recruit Beck. (The village is near your party's starting point in the middle strip of land. Go to the village fast! A thief is on the map and he will rush the village and destroy it if you give him a chance.)
 * Defeat the two upper units with regular attack units like Ogma and Wolf.
 * Use Beck to destroy most of the ballistae in the middle. Then, move in and defeat the remaining units.
 * Kill the boss; Beck can do this alone.
 * Visit the houses (see above for exact details).

Beck moves one forest square at a time, but his incredible range lets him destroy effectively. He is effectively constrained to moving horizontally along the small strip.

Leave your other units to wait and let him take out most of the ballistae. Watch out for the boss, but even he can be destroyed by Beck.

By now, the main path should be clear enough to go ahead and recruit Astram. You need Midia to recruit him.

The boss for this chapter is Grigas:

Beat the last few units and seize the gate. Save the game.