Plot hole: Bonnie is the anchor for the other side and feels when supernatural beings die. How come she didn't know Katherine wasn't dead? Did she never think it was suspicious that she never felt Katherine's body after she died?
Suggested correction: Katherine died but didn't go to the other side. So she didn't need to go through Bonnie. She went to hell to Arcadius. Bonnie is not the anchor to hell, we don't know how going to hell works.
After everyone finally realises that Elena had been possessed by her Doppelgänger Predecessor, It is actually shown that Katherine were more or less dragged away from Bonnie before she could crossover to the Otherside. So we do have some idea as to how one ends up in Hell.
Suggested correction: Katherine was a human technically when she died.
Technically, she was supernatural because she was a doppelganger, so she should've gone through Bonnie.
And even she was a traveller.
The Bank Job - S3-E1
Plot hole: When Toby, McCluskey, and the others are looking at the bank's security camera footage, Toby asks to zoom in on Newman's tattoo, and then Toby asks if he can borrow someone's cell phone so he can ask Oz about the bank manager. It cuts to Oz at the hospital as his cell phone rings - when Oz picks up his cell he presses the button and promptly says, "Hey, Toby, what's up?" It's quite impossible for Oz to have known that it was Toby calling him if Toby was using someone else's cell, and he did not even have the chance to hear Toby's voice. Those telepathic abilities belong to Toby, not Oz.
Plot hole: Dillon was quickly identified by the city sensors as having metal parts, thus classifying him as a threat to the city. Yet Tenaya, who is essentially a cyborg, tries out for the Green Ranger without setting off the same sensors.
Suggested correction: Tenaya wasn't caught because the guards assumed the equipment was faulty. It was giving positives all day because of all the sleeper agents we find out about later.
Plot hole: The White Knight is knocked out by a bomb in his attack on the casino. When he regains consciousness, he fires one last crossbow shot, which he thinks destroys the casino. But who loaded and cocked the bow for that last shot? Crossbows don't reload themselves.