Continuity mistake: When in the rowboat, Adrienne Barbeau's t-shirt is white in some shots and blue in others. It is not the lighting - it is plainly two different coloured t-shirts.
Continuity mistake: When the Swamp thing goes to destroy one of the trucks chasing Cable, the trucks used are chevy blazers but the one he wrecks is a International scout.
Continuity mistake: At the end of the film Cabel gets stabbed in the right side of her décolletage, and she bleeds all over her evening gown, as you would. Swamp Thing very kindly heals the wound. Apparently he also has the power of magic dry-cleaning too, because the blood disappears from Cabel's dress.
Continuity mistake: Between Cable being nabbed by the bad guys and escaping by leaping overboard from their boat and the scene where she watches Swamp Thing having his arm chopped off, she alternates between wearing a fairly obvious bra and, well, swinging free, as it were.
Revealing mistake: When the Swamp Thing walks past a bush, it's camouflage netting.
Continuity mistake: When the guy chops Arcane's arm off in the swamp, he chops it off between the wrist and elbow. As Arcane walks away, his arm is chopped off up by his shoulder.
Continuity mistake: When Bruno drinks the formula he shrinks and so does his clothes.