User blog comment:EmpyreanSmoke/Supernatural Q&A/@comment-27006668-20151002194202/@comment-26982641-20151003092248

2- Its written that Lucifer created mark and gave to cain, no one except death and archangels know that god created mark

4-According to pagan and angels' strength

5- Who knows maybe he might helped god and granted him complete immortality so darkness won't be able to kill him (theory)

6-Yes

9- They were low tier demons pal also mark empoweres first blade, if you know how to use mark efficiently, you won't need first blade. (As you can see he could smite)