Opening battle: 2 horsemen are hit by fireball mortars and fall from their horses. Moments later, the same horsemen are hit by arrows and fall again. It's the same footage - reused.
The previous two "Transformers" films both earned over $1 billion worldwide at the box office, and this fifth film was considered such a guaranteed hit, nearly a dozen more films set in the "Transformers" universe were planned before its release. However, the movie ended up bringing in the lowest grosses of the entire series, and has as of July 18, 2017, only brought in just over $500 million worldwide- only half of what the previous two films earned.