Highlander II: The Quickening (1991)

Highlander II: The Quickening (1991) commits the cardinal sin of retconning its immortals into aliens from the planet Zeist, dismantling the original's mythology. Even director Russell Mulcahy disowned the theatrical cut—a rare admission that highlights its catastrophic 0% Rotten Tomatoes score, 17 points lower than #6. With a budget of $30 million and a domestic gross of $15.9 million, this sequel lost 47% of its investment, worse than the typical franchise blunder. Its convoluted plot and production conflicts make it a cautionary tale of creative interference run amok.