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)
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)
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.
Continuity mistake: When Han is speaking to Lando before he departs for Endor, the distance between the two men changes between shots.
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.
Continuity mistake: Outside the bunker the position of the bodies keep changing or moving throughout the battle on Endor.
Continuity mistake: When R2-D2 is shot by an Imperial stormtrooper whilst trying to open the shield generator's doors, he goes into the side wall and you can see a door open on his body with an interface arm sticking out of it. But when Han shoots the stormtrooper dead, we cut back to R2, and the door that was originally open is now closed.
Continuity mistake: When the Rebel fleet is preparing to make the jump to hyperspace to the second Death Star, the small fighters move first. Then the big ships. But when the big ships move into hyperspace, there are only the Medical Frigate, some transports and some Blockade Runners. What happened with the big Correllian command ships?