I wanted to make another assassin but I didn't want to make the same old "sneak around stab everyone in the back" assassin. I was thinking gabout adding alchemy and maybe some magic into the mix and I wanted some tips on how do do this effectively.

For my assassin build I invested in the poisoner perk in alchemy and the poisoned perk in pickpocket. So I can sneak in their houses while they sleep and poison them
the only magic that I use in this build was was enchanting if you count it as magic and not a skill

You can also use Illusion, Frenzy and Pacify are great spells.