When the worm comes out of its hole, shoot the claw-like hands at the end of each tentacle-like arm. They should eventually turn red. Continue firing at them and they will snap off. When it snaps, the worm will go back in its hole. Run inside after it, but stop at the edge so you don't fall in the lava. Look around to find the body of the beast, then look closely to see a big eyeball-like thing wiggling around. Shoot it until goes in, then the arm that snapped will regenerate and come back out. Shoot the arm and, when it snaps, go back in and shoot it again. When the arm stops coming out, go for the other arm and repeat the process. Note: If you have a rocket launcher, use that and the battle will over much quicker.
Hold start and press the indicated button to perform the corresponding taunt in multiplayer mode. The first three taunts are the same for all characters. However, the fourth taunt(holding start and pressing left) is different for each character:
HOW TO PERFORM
Hold gun in the air.
Hold Start and press DOWN
Say "Let's go"
Hold Start and press UP
Say "Oh yeah"
Hold Start and press RIGHT
Hold start and press left to perform the listed taunt for the corresponding character:
Make sure you gather as much thermal energy as you can. On your way up the mountain, destroy all of the Akrid hives and get the rocket launcher on the metal slab jutting out of the mountain. You can also get the large VS laser if you want a back up. Then, climb to the top of the mountain, but do not go into the cave. Instead, stand at the top and wait for the moth to fly over you. Aim at the orange weak spots and shoot the tail part with your rocket launcher about two times. After the tail falls off, do the same to the wings. A couple more weak spots will appear near the top of his head. These are easier to hit with a charged laser shot. When the moth crashes into the side of the mountain, the achievement will not appear. However, you will unlock it after you complete the mission.
As soon as the fight begins, notice the VS will fly around while doing various little spinning attacks. Fly towards him while holding L2, then release when next to the Boss (to do a horizontal slash). You'll take a significant amount of health from the Boss. Sometimes you can also score a second hit this way, but be cautious of the homing missiles. The Boss will dart around shooting little lasers at you, which are easily avoidable by simply following in his direction to miss the attack. When the boss reaches around 30% health it will call up two laser weapons that do massive damage if they hit you. One is horizontal and the other is vertical. Notice when he gets ready for this attack that he will throw his arms forward. Use it as your cue to get as far back as possible. The range on the lasers are fairly small. When he is done, he will stand still for a brief moment and shoot missiles from his shoulders. Take this opportunity to go in and deal some damage. The Boss does not have much of a pattern. Remember to hold L2 until you are directly on him and release. Around nine well-placed slashes are required to defeat the Boss.
Before you fight the worm, gather as much thermal energy as you can. Get more thermal energy by destroying the surrounding heat tankards and activating the outpost. If you need more thermal energy, simply kill the surrounding flying Akrid and their spawn points. Get a sled VS and attach either a rocket launcher or gatling gun (recommended), then ride it just to the entrance of the Snow Plain. If you ride it any further, the worm will knock you off and destroy the VS. Once you get off the sled VS, take off the weapon you brought with you. The gatling gun is recommended because you can adjust your aim and keep shooting him if you miss, unlike the rocket launcher. Wait until he emerges from the snow and be ready for him to either growl or charge at you. If he charges and hits you, consider yourself dead. You can either roll to the left or right. After rolling, aim at his sides and you will see a number of weak points. Shoot at them until they explode and reveal a reddish boil. Repeat this until they are all gone, then switch sides. Once he is hurt enough, he may start shooting flaming balls that explode from his backside. Be sure to evade them. You will once again see more weak points. Do the same thing as done with his head side to finally kill him. He will leave behind a large deposit of thermal energy when he dies. The worm will re-appear no matter how many times you kill it. Also, the achievement for killing it will not appear until you complete the level.
The useful anchor that everyone uses to reach high places can be used a bit further if you press X + SQUARE instead of just SQUARE. This only results in a slightly further distance, not a significant one.
Fight your way up to the building to the left from your beginning viewpoint and, when at the back of the building with the stairs, go to the top or just stay on the ground. Notice a large wall with a nice designed bar gate. Press Y while aiming in the middle area where there is snow. Once at the top on this ledge, aim at the tip of the gate. Reach to over the gate to skip the fight with the large mech below the right building.
When taking heavy fire and need to replenish your health (if you have the thermal energy), hop into the nearest VS. You will be invincible for about five seconds while it is doing the startup animation.
A VS with two empty arms and two Gatlin guns are required for this trick. Attach both guns to each side of the VS and fire only one of the guns a couple times. Then, start firing the second gun. If done correctly, one of the guns will reload while the other is firing, causing the guns to never stop firing until you run out of ammo or manually reload. This works great against any Akrid Boss, especially the one in Mission 05.
Use the rifle that you find at the start of the level to snipe the head of the rider of the VS. It will take about two or three shots, but he returns to the same position for an easy snipe. Disregard all of the other people shooting at you and run to get into the VS. Kill your way to the end of the map, then get out of the VS and go through the door. Once in the next part of the level, run to the VS that's on the ground forward and slightly to the right of you. Destroy the other VS that are trying to destroy you. Note: The Boss VS is the VS jumping around.