And Then There Were None - S6-E16
Revealing mistake: Samuel is very much dead, laid out on the table in the canning factory employee lounge, but as Sam stands over him, talking about whether or not it was right to gank him, you can see Samuel's chest rising and falling as he breathes. (00:26:30)
Hell House - S1-E17
Revealing mistake: Dean gets his phone and snaps a picture of Sam when he's asleep. You see his phone take the picture but the screen is then white, showing he didn't really take anything.
Born Under a Bad Sign - S2-E14
Revealing mistake: When Dean turns over the deceased man lying on the floor, the man blinks while Sam and Dean are arguing about whether or not Sam is responsible for his death. (00:10:25)
Revealing mistake: Dean borrows Charlie's phone to call Sam. On the phone, the lock screen can be seen, showing that he never entered in any number.
Fresh Blood - S3-E7
Revealing mistake: Dean cuts himself near the beginning of the episode, however the blood begins to drip (spurt really) before the blade cuts into his arm.
There's Something About Mary - S12-E21
Revealing mistake: At the start of the episode when Dean calls Ketch, Dean's phone is not in Call Mode.
A Very Supernatural Christmas - S3-E8
Revealing mistake: When the boys are tied up and the pagan gods are preparing for the ritual, the second time they cut into Dean's arm the knife is pressed along his arm and the blood is removed showing no cut at all.
All Hell Breaks Loose: Part 2 - S2-E22
Revealing mistake: Sam is breathing noticeably at the beginning of the show on the bed even though he is supposed to be dead.
Fresh Blood - S3-E7
Revealing mistake: Sam takes the SIM card out of his phone so it can't be tracked, but when he takes the back off his phone, there's no battery, and the SIM card is just lying in the back not attached to anything! Same for Dean's - he takes the back off and the card just falls right out, not secured in any way as it would be in a real phone.
Revealing mistake: During the love scene between Dean and Cassie, you can see the tape used on Cassie to keep the show PG-13. (00:23:15)
Revealing mistake: As Dean digs into the dead guy's guts and discovers the claw the pale dead guy blinks.
Revealing mistake: When Sam pulls Angela out of the bathtub and on to the floor, you can see the panty line from the nude colored panties she's wearing to keep the show PG13.
Revealing mistake: When Dean cuts leviathan-Dean's head off, if you look closely you can see that a) the decapitated head disappears while it is still in the air, and b) when the body recoils, its hands disappear.
Revealing mistake: When Max opens the bedroom door to confront his step-mother and Dean, using his telekinesis powers, you can see the equipment used to open the door, a rope pulling the door on the floor. (00:34:19)
Hibbing 911 - S10-E8
Revealing mistake: Sam types the address Donna gave him into an untitled note, which is supposed to act as a Maps search engine. A second later, a map with the address pulls up. His phone also says it's 9:56/9:58 a.m. (00:31:15)
Revealing mistake: When the woman is under the bed with her baby her arm is covered in blood, but when she touches the baby's face and clothes, no blood comes off onto the baby.
Children Shouldn't Play with Dead Things - S2-E4
Revealing mistake: When Dean is talking to the girl about Angie, she's crying hysterically and using tissues yet there's no tears coming from her eyes.
Revealing mistake: After Sam (Lucifer) beats the crap out of Dean's face, when he's sitting on the ground, you can tell he's got something stuffed in his mouth to make his cheeks and lip look swollen.
Revealing mistake: The guy gets a pack of raw hamburger out of the fridge and starts shoveling it in his mouth. We can plainly see it's just red jello.
Answer: Angel blades come from angels. It's their angelic magic that makes it special. Therefore, an archangel blade is made magical with the powers of an archangel. They couldn't have just created one or used one, as none of them are archangels.