After you obtain the Varia Suit in Artaria, you return to Cataris, where you can explore the areas of extreme heat.
Explore the Area of Extreme Heat
From the red Teleportal, go to the left to fall through the Pitfall Blocks there. If you wish to save, go through the door on the left and use the Save Room, then leave the Save Room and go to the right. In the next room, shoot your beam to the right to destroy the block at the end of the tunnel, then roll through the tunnel. In the next room, shoot toward the right to destroy the blocks in the way. Go down to the door, open it, and go through.
Shoot to the left to break the blocks above the lava, and jump over the lava after the creatures that shoot out of the ceiling have gone past. Go to the left and down, then go to the right and roll through the tunnel.
At the end, kill the creature below (if you get close to it, you can watch for the flash, then do a Melee Counter and shoot your beam to kill it), then slide through the tunnel on the left and kill the creature in the next room. Climb into the tunnel at the left side and roll through it to reach the next room.
Go to the left and drop down below, then jump over the two lava pits to the right. Slide under the wall on the right, then shoot the middle of the right wall to break open a hole. Roll through it, then go to the right and kill the creature, then shoot the top of the wall to the right and roll through the hole that you reveal. There is yet another creature to the right, and this time the wall on the right has a red thing in it. Shoot it, then roll through the tunnel that is revealed, to reach the next room.
Jump over the lava to reach the ledge on the right, then shoot the red thing in the wall to reveal another tunnel. Roll through it, then jump onto the blue wall on the left and use it to land on the ledge on the left. There is a creature on the door to the left. If you get close to it, you can watch for it to flash, and perform a Melee Counter to kill it. It will drop a lot of health/ammo if you do this successfully. Afterward, go through the door.
Go to the left and shoot the red thing in the wall. Then roll into the lowest of the two tunnels on the left. You will fall through the floor and there will be a cutscene.
Shoot missiles or charged shots into Kraid's open mouth. If Kraid's mouth is closed, shoot its face to make it open its mouth. It will periodically throw claws at you, which you can destroy with missiles and charged shots. It will periodically raise its head and spit blobs and fireballs at you. The blobs can be destroyed with normal shots, but the fireballs can't be destroyed, so move left or right on the platform to avoid letting them hit you.
Eventually, there will be a cutscene. Afterward, shoot the purple thing on its belly with normal shots. The purple thing will periodically shoot a purple blob out, which will create a wave of purple ooze on the ground. Jump so that you land in the middle of the wave after it separates. The purple thing can also spit out blobs that bounce around on the platform. You can destroy these with missiles and charged shots. Avoid letting them touch you.
Kraid will periodically launch platforms at the wall. Jump upward to avoid getting hit by them, so that you land on them. They will take you to the upper part of the room, where you can grab a blue wall and shoot Kraid's face to make it open its mouth, and you can shoot missiles or charged shots into its mouth to damage it. Kraid may also throw claws at you at this time that you will have to shoot with missiles or charged shots. While you are on the blue wall, Kraid may move its left arm in front of it, which means it is about to flash, allowing you to do a Melee Counter. If you succeed, shoot missiles and/or charged shots until you jump back onto the blue wall on the left. If Kraid doesn't move its arm in front of it, watch for its eyes to glow red. This is your cue to fall back downward, because Kraid will soon punch the wall that you are holding onto.
Kraid may block the purple thing on its belly with it hand. It will then shoot out three platforms, but these are not spaced such that you can jump onto them, so instead, you should crouch down to avoid them. Then, the blue wall will come down to you. Grab it and it will take you to the top, where you can shoot into Kraid's mouth like before.
Repeat these strategies until there is a cutscene and the battle ends.
Get an Item Sphere
Jump onto the platform on the right, then jump up and grab the blue wall on the right, then go up and jump onto the blue wall on the left. Climb up and enter the tunnel to the right. Roll through to the next room.
After you go through the end of the tunnel, go down to the bottom of the room (be careful of the creature that flies out of the wall on the right), then turn left and shoot a missile at the Missle Cover over the door, then open the door and go through. Shoot the item sphere that the statue is holding, then take the item to get Diffusion Beam. Your charged shots will now create an explosion that penetrates a short distance through walls.
Get a Missile Tank
Shoot a charged shot at the red thing in the ceiling on the right to break open a path. Roll through the tunnel on the right to reach the previous room.
Jump onto the ledge on the right, then shoot charged shots at the red thing in the wall above and to the left until a new path opens. Go up through the tunnel at the upper left. Then go to the right and you will find a Teleportal. Before you use it, there is an upgrade that you can get. Jump up to the ledge on the left, then jump up onto the ledge on the right. There are small ledges to the left that you can grab. From the ledges, jump to the right, then change direction so you go up to the next small ledge. Kill the fireball-spitting creature on the wall on the right, then jump upward using the small ledges on the left until you can jump onto the blue wall. Shoot charged shots at the red thing in the wall on the upper left until it is destroyed. Then jump up into the tunnel that you revealed and roll over to the Missile Tank.
Use the Teleportal
Afterward, go back down to the Teleportal and use it to return to Dairon.