When Postmaster P is singing "Stray Bullet to the Heart" he removes his jacket twice.
When the group of musicians at the start of the movie are shooting the leprechaun one of the guns clearly goes into the empty position where the barrel is exposed but in the next scene the gun is shown firing again even though no more bullets were put in it.
In the beginning of the movie the leprechaun is being turned to stone, the gold medallion is also turned to stone.The rest of the movie it is gold.
When Post proves to Stray that the flute is magic Stray starts to move his hands to his ears before Post asks him to.
After the group is told that they made it to the finals and celebrate, you can see the top of the sets walls and see the other room behind it.
If the Leprechaun was turned to stone in the 1970s and was not reverted to normal until present day, that would make the events of Leprechaun (1992), Leprechaun 2 (1994), and Leprechaun 3 (1995) impossible, as the Leprechaun would still have been stone (this time line error does not affect the events depicted in Leprechaun 4: In Space (1996), as that movie took place in the future).