Through the Wall of Ice
MAP: Ice Forest Shalala
BGM: Kachinkoron's Theme"The low ceiling of the Ice Forest Shalala makes spears and bows useless... and beware of the pressurized snowball cannon! Put Tatepons on the front line with Kibapons in the vanguard."
As the description states, ranged weapons are useless here. Field your best freeze resistant melee fighters. If you have Toripons they can be of help because they shoot from the air to the ground so the ceiling doesn't bother them, they are also out of range of the snowball machines. Don't bring a Toripon hero though as the Hero mode is wasted if you are in a tunnel.
Alternatively, bring Tatepons, Kibapons, any other unit type and a Dekapon Hero (that has a freeze resistant mask will help as well). If Hero Mode is activated, your Dekapon hero starts spinning his hammer, pretty much killing any unit in the way in one or two hits. It is ridiculously effective against the Akuma Kibapons which simply charge to their doom and the enemy Tatepons are also shredded relatively quickly. As long as Hero Mode is up, Pata-Pata-Pata-Pon should let you cut through everything quickly.
When you start the stage, you come across a Karmen fort with a snowball machine behind it. The snowball machine freezes your guys so freeze resistance is a must. After dealing with that, you come across the first of the tunnels. Each of the tunnels have walls you have to break down. After you get out of the first one, you meet your old friends, Dark One and Black Star. They are amused that you are 'clinking' up here. After keeping it up through some more tunnels, General Kuwagattan shows up to give you a pounding. He does average damage. Defend against him and the Akuma Kibapons are important kill targets. Smash through the last Karmen fort and everyone will leave, letting you complete the mission.
"That's our Great Kami! Victorious even in the freezing cold!! Everyone, give praise to the great one!"
Through the Wall of Ice Lv. X
"I'f you can't put your full force in the vanguard here, you many want to avoid large creatures. Hero whispers. "Use Megapons with a Tailwind..." This is the repeatable fortress siege. It will not be available directly after beating the previous stage, but will appear after completing another stage. Defeating this the first time will give you the Mysterious Egg for the level. The Dark One, Black Star and Kuwagattan will not show up.