When the Evil Alien Slayer sets the timer bomb for 60 seconds, the clock numbers are right side up. But when Bruce Banner cancels the sequence later, the clock reads upside down.
When the Hulk is being laser blasted by the Evil Alien Slayer is in Banner's mind, he briefly appears with Grey Hulk's character design.
After Dark Hulk tosses a tank at military vehicles, there's an areal shot where the green Hulk is visible instead of Dark Hulk.