I captured each flashes of the crystal (I think so) in the 5.12 episode. Very easy to find the origin of some of them, but some are really difficult. I'm waiting for your answers. Are you a great connoisseur of the whole show ? Give it a try. I will give my answers tomorrow.
Congrats @Auroradawn 89 ! You have an excellent knowledge of the whole show :
1. Excalibur - Merlin sets fire to the wraith. I DON'T KNOW WHAT IT IS
2. The Tears of Uther Pendragon - Kilgharrah rescuing Merlin from the serkets
3. The Crystal Cave - Morgana attempting to kill Uther
4. The Gates of Avalon - Arthur drowning
5. 4x01/02 - The Dorocha
6. 1x13 - Nimueh's fireball
7. 3x13 - Excalibur and Freya
8. 4x01 - Merlin attacked by the Dorocha
9. 3x08 - Water from the Lake of Avalon
10. 2x13 - Merlin taming Kilgharrah 3x05 THE DRAGON GIVING MERLIN THE POWER TO CURE MORGANA.
11. 4x13 - Emrys and the poppet
12. 5x06 - Morgana kidnaps Gwen I'M NOT SURE. I DIDN'T SEE THIS IMAGE IN THE 5.06.
13. 3x05- Before Morgana falls down the stairs
14. 1x05 - The griffin is killed? AITHUSA BREATHING FIRE IN 5.09
15. 2x08- Arthur's test
16. 1x04 - Merlin dying
17. Can't tell - the image is too vague WE SEE THE POPPET ON THE LEFT AND A KNIGHT WITH A ROLL PARCHMENT IN HIS HANDS ON THE RIGHT
18. 2x13 - Balinor being stabbed by Cenred's men
19. 3x08- Arthur riding out for his quest
20. 1x11 - The unicorn and Merlin
21. 1x07 - Arthur in Morgana's dream
22. 1x09 - The wraith interrupting Arthur's ceremony
AT LEAST 17 GOOD ANSWERS ON 22 AND PERHAPS MORE IF YOU'RE RIGHT ABOUT THE N° 1
Not bad @ Agnes Flether, I would say 14 good answers.
BTW, I missed five flashes. Here are they :