The Return - S2-E1
Continuity mistake: Elena's house address is different. In season 1 episode 1 Elena's house number was 935. In this episode Elena tells the ambulance that her address is 2104 Floyd Street. (00:39:30)
Continuity mistake: When Caroline is talking to Stefan at the party, her eyes are made up very dark. In the next scene, where she talks to Matt and Amy, her eye make-up is a lot lighter.
Masquerade - S2-E7
Plot hole: Why did Stefan and Damon suddenly decide to abandon their plans to kill Katherine when the spell linking her to Elena were broken? When only moments earlier, Damon said "The second the spell is lifted, I'm gonna drive a stake right through your heart." So that begs the question why did he never follow through? Why instead place her in the spelled tomb that you know can be dispelled? It makes absolutely no sense when you think about it.
Answer: Silas did mention to Bonnie later that he was so powerful he was able to overcome Jeremy's hunter's curse in minutes.