Continuity mistake: When Lando orders half the fighters to break off and return to the surface, an A-Wing and an X-Wing break off to the right. When Green Leader acknowledges, the same A-Wing and X-Wing break off to the right again.
Continuity mistake: When R2-D2 cut the net, only Han, Luke and Chewbacca fall from it. Maybe C3P0 would have hold for a moment because his leg was stuck in the net, but R2 was right over the hole.
Revealing mistake: In an overhead shot of Darth Vader throwing the Emperor to his death down the Death Star reactor, you can see that it is a dummy in the Emperor's costume and not Ian McDiarmid.

Continuity mistake: When Luke is riding the speeder bike against the trooper, the black glove on his right hand jumps to his left and then back again. (01:01:15)

Continuity mistake: During the fight between Luke and Darth Vader, when Vader throws his lightsaber at Luke, it is not only Luke's lightsaber from Episodes IV & V instead of his own, it is ignited upside-down, with the blade protruding from the pommel rather than the emitter. (01:50:20)
Revealing mistake: In the scene where Han and Chewie sneak up on the two storm troopers on the Endor moon, Han steps on a twig, it snaps, and the trooper turns around and punches him. Watch in slow motion as the punch is released, Han starts falling backwards before the fist hits him.
Suggested correction: If you have to use slow motion to see something, it's not a mistake.
Audio problem: After R2-D2 gets shot, Leia says to Han, "I'll cover you.", but the words don't match the movement of her lips. (01:39:00)
Audio problem: When the shuttle Tydirium is approaching Endor, look closely when Han says, "Fly casual" - he begins to say the words before his lips start moving. When he stops talking, his mouth is still moving.
Revealing mistake: When the Tydirium shuttle is flying toward the imperial spaceships, there's a frontal shot of it and a strange thing appears near the shuttle for a few frames. It's not the kind of marks that appears on an old film, or a special effects box. It's like a problem with the mate painting.
Continuity mistake: When Anakin Skywalker (Vader) dies, the path of a tear is visible under one of Luke's eyes. Two shots later, the tear path is dry. (01:55:45)
Revealing mistake: When Luke jumps from Jabba's prisoner's skiff over to another skiff, if you watch Lando hanging underneath the prisoner's skiff, you can easily see that he is a matte painting in this shot, because he doesn't move at all.

Continuity mistake: Vader tosses the Emperor and then collapses on some barrels next to the railing. Look at Vader's arm - the one with the severed hand. His arm is bent at the forearm in a way that arms just don't bend. This is because David Prowse's hand was inside an "elongated" arm to simulate it being chopped off. He couldn't keep his wrist straight, giving the appearance of a bent forearm. (01:57:00)

Revealing mistake: When Jabba's sail barge begins to explode, you can see that one of the floating skiffs is standing on stilts. (00:36:30)
Continuity mistake: In the scenes where the Emperor is trying to convert Luke, watch the stars through the window behind him. The same group of stars go floating past every time.
Continuity mistake: Look at the full body shot of the holographic Luke. Luke, who normally has his lightsaber clipped to his left hip, now has it hung from his right hip. As well, his hair, which normally has a part on his left hand side, is now parted on the right. Afterwards, just before Artoo turns the message off, we get a shot from behind Artoo, and Luke's hologram is visible on the extreme right of the screen. Luke's lightsaber is now hanging from his left hip where it normally is.
Other mistake: On Endor, after Han Solo's group was captured, C-3PO called out to the Empire's soldiers. One of them said "Bring those two down here!" Both C-3PO and R2-D2 were up there, but from the Imperials were standing, they could only see C-3PO. R2 was hidden behind a tree. They wouldn't know that he was there until they actually got close to the two.
Continuity mistake: When Han is speaking to Lando before he departs for Endor, the distance between the two men changes between shots.
Revealing mistake: The interior matte painting of the hangar on the Rebel ship holding the stolen Imperial shuttle doesn't match the appearance of the hangar from the exterior shot of the Rebel ship. The interior hangar shows an extended platform and four banks of vertical lights bordering the opening and then walls. From the exterior, the hangar appears to have a big light bank near the opening, and then thinner light banks behind it spaced further apart than the interior shot. The exterior shot also doesn't have a platform. (00:50:45 - 00:53:20)
Revealing mistake: When Luke and Leia swing from the deck on to the skiff, you can see that the man playing Lando Calrissian is not Billy Dee Williams but his stunt double. (00:36:25)
Continuity mistake: Before the rebels take off for Endor, Han says to Lando to take the Millennium Falcon as "she's the fastest ship in the fleet". At this point, Lando can be seen moving his head down, but as the scene changes he is looking straight ahead again.