Chapter 4 - Lair of Grievous
Start moving up the screen, towards the mist. Stick to the left side of the pit, thanks to which you will eventually come across a ship with soldiers . Call them using the Commander's radio and move on. You will reach a passage in the rock. Use the bazooka to destroy the container on the right side of the gate .
Afterwards order the soldiers to shoot at the containers on the left . Once it's destroyed, enemies with bazookas will appear on the left and right . It's best to respond with rockets.
After dealing with them, use the trooper's hooks on the grapple points on both sides of the door . Once the gate is unveiled, use Force to match the bricks with the purple stands .
Go inside and start going deeper into the corridor . At some point you will reach a gulf. On the walls on the left and right you will find two platforms, place them on the purple pillars sticking out of the lava .
Afterwards jump across the platforms  to the other side, where you will have to fight some enemies .
After you defeat them you will have to get across another pit . Once again use the platforms sticking out from the walls. After you get to the other side, keep going forward all the time .
After the animation you will reach a long corridor . Continue moving forward until you reach a door. Open it with the power plugs .
Defeat a few enemies in the next room and then use the grappling hook on four orange bolts  on both sides of the door. Afterwards use the bazooka to destroy the nearby "metal" containers .
Note that quite a lot of bricks have appeared on the floor. Use Force on them and move to the shape by the door . You will be attacked by Grievous. While looking out for his swords, go to the lower edge of the room, where there is a box with grapples. Pick it up using the Force and throw at the enemy .
While he's stunned, quickly switch to Commander or a soldier and use the grappling hook on the enemy . Keep repeating this until Grievous starts attacking you from the ceiling. All you have to do then is pick up the box and throw it at the enemy .
Once he falls down, approach him and attack with the Saber a couple times . After he runs away, enter the dark tunnel .
Inside the next room, stand on one of the red buttons  and wait for your companions to do the same. After you fall down, be careful now to fall into the lava. At the same time use the Force to arrange the bricks  so that you can get out of the trap.
Once the construction is ready, just jump to the surface  and go right. On the arena you will have to fight another boss. Keep dodging his attacks and once you're ready, use the grappling hook on the orange grapples in his thighs . Remember that you have to use two characters with grappling hooks to do that.
After immobilizing the creature, switch to a Jedi, stand on the blue circle in front of the beast  and attack it. Keep looking out for his attacks  and repeat the process until the beast falls.
After the fight head into the tunnel  and follow it outside. By the landing zone you will have to fight a few enemies. Once you kill them, unplug the generator  and push it towards the round platform in front of you.
Afterwards build an antenna fastening from the bricks on the left  and place it on the left tower  (you need to take off the round pole beforehand).
Afterwards connect the plug to the generator  and place the antenna on the tower. Grievous will enter the arena in a bit .
Dodge his attacks by jumping across the arena . Eventually a friendly ship will arrive . Jump onto it to end the mission.