Part 3, Chapter 6 help

This chapter is all about defense, although the victory condition is to kill 46 enemies. This because there is darkness everywhere, and far moving sub human enemies can take advantage of that. In order to win, keep your units and your allies close together, bloackading the passages to your advantage. Wait it out until the Black Knight arrives, and at that point send him out to slaughter enemies, but as Greil would say, "Stay back!". This is very good advice because although the Black Knight is there, your not home free yet. When I first played this chapter, I over advanced my army thinking I only needed to kill one enemy, but the enemy survived the attack and kill Micaiah. I'm not sure how far you can advance on easy, but I really doubt you can get any of the coins on normal, and don't even try on Maniac (hard) mode. Not like coins are that important anyway. If you still have problems, let us know what your party is, what supports you have, etc.

No problem, these types of chapters are hard if your not prepared for them.

Yeah, I always had the allys go to the east part of the blockade, because that will be where you are weakest. If you don't have the east blocked off with allys and your fronlining units, keep all weak/ranged attackers to the north where it is easier to blockade. That way the enemy units have to travel around the allys and up to the northern blockade to attack weak units.

Do not put ally units on halt. In fact this is the only map where they should be roam. The reason is there are 2 bishops with Physic, and for some reason the AI seems to be slightly better on this map in that the ally bishops actually heal your player characters. This is very important because unless your Nolan/Edward/Aran are high level 2nd tier or entry 3rd tier, they will die in 1-3 hits from the transformed Laguz, Edward will die in 2 hits for sure due to his totally messed up dodge chance and low defense. You do not get any bonus EXP from surviving allies, so why not let them kill a few enemies? If they just sit duck there they'll be killed in 1 or 2 turns anyways. Have your strongest units create a chokepoint based on the environment blockades (tree stumps) and make sure to stay in bushes as often as possible. Have Laura at the north side and Micaiah at the east side right behind the frontline units to heal, and they're completely safe since no Laguz has ranged attacks.
If you use this strategy, and assuming your Ed/Nolan/Aran aren't ridiculously low leveled and one of them has the Beastfoe skill, you're actually gonna be able to have one of the above 3 units advanced far north onto that island and start actively seeking out Laguz to kill.
Dawn Brigade missions are always more challenging (and more fun), but the annoying part is most of DB members have pathetic growth rates, so in anger I often have to reset my Wii to get a better stat grow. Ike's team have generally far too easy missions because not only do you get Laguz support most of the time, but all of the units are at least 2nd tier and some may be in their 3rd.