Continuity mistake: When Gru is attempting to unlock the floor key pad, he triggers an incorrect key and some fire is blown at him. Some smoke is left all over his face. Gru triggers another incorrect key and some darts are launched at him. The smoke is still there, but as he falls over, most of the smoke on his face has gone. The smoke on his right cheek is still there, but has still vanished from his face. (01:04:20)
Plot hole: The rocket is launched with Gru and Lucy attached to it. All of the minions are around them at El Macho's lair at this point. Considering a rocket travels at several hundred miles per hour, when they jump off it almost a minute later they should be several miles away at the very least, but three Minions appear on a boat shortly after. There is no way the three Minions could have reached Gru and Lucy all the way from the lair in that short time. (01:22:05 - 01:23:25)
Other mistake: When Agnes screams after the evil minion tries to eat her unicorn, the noise shatters glass items and a sculpture on the mantelpiece as well as the evil minion's goggles. But Margo's glasses do not appear shattered at all.