The Elder Scrolls V: Skyrim Special Edition

Great guide above by PraXis91x for the Sneak skill; however, if you're already past that part of the game and/or fancy a bit of conjuration to level 100 with minimal effort, then check out my video below! :)

If you don't mind cheesing it, you can earn this easily doing the Dragonborn DLC, and you'll need 11k gold.

1.) Play the story until you are summoned by the Greybeards, and acquire the horn, and finally return to the Greybeards, being fully recognized as Dragonborn.

2.) Run around until you are accosted by some cultists who look like they have a Cathulu mask. Answer them, doesnt matter what you say. Kill them and loot their corpse for a note.

3.) Head to Windhelm, then to the docks for passage to Solthesiem, when able, head South-South East to find Kolbjorn Barrow. You'll run in to Ralis, who asks for some money, agree.

Steps 4 and 5 in more detail


4.) Fast travel back to Raven Rock, and while inside, wait for 48-60 hours. Go outside and a courier will give you a note to return to Kolbjorn. Talk to Ralis, and kill Draugr.

5.) Repeat until you deal with Ralis. In the area you fought the Dragon Priest, continue through the crypt to find a Black Book.

6.) At the end of the bool, select "Secret of Arcana", a Power that reduces mana cost to 0 for 30 seconds.

7.) You now need the spell Telekenesis. This can be acquired easily at Benkongerike, which can be found on Solthesim, to the southeast of Saering's Watch (a Dragonborn DLC plot location) or to the northwest of the Headwaters of Harstrad at about the halfway point between both locations.

Just after entering Benkongerike Great Hall, to the right, in a tent, is a pile of thirteen copies of The Lusty Argonian Maid Vol 1 and six copies of The Lusty Argonian Maid Vol 2, and under these books is a Spell Tome for Telekinesis.

8.) NOW, with "Secret of Arcana" as your Power, and Telekenesis equipped, find an item, use your Power, and use Telekenesis. While using Telekenesis, bring up the map and fast travel. As far as you can (you can do this in Skyrim, usual Riften to Dawnstar or vice versa is fine). This will raise your Alteration to 100.

Simple solution for once you have reached High Hrothgar. Simply bring a a weak damaging knife (I used an Iron Dagger) and find a Greybeard sitting in prayer. Then turn up the difficulty to legendary and sneak up behind the Greybeard and attack him.
Due to the high difficulty and the weakness of the dagger, they will not attack you in retaliation whilst you are undetected. This will send you sneak up at a fast rate.

They will stand up eventually, but you will be able to keep going. That said though, they will turn around after a while, so be careful as this will cause them to attack you, so regular quicksaves are recomended just to be safe in case. Beyond that, Just keep going until you reach Lvl 100.

Can do Sneak skill real easy, althought the technique is boring.

Go to any bar in the major cities, the best ones are Riften, Solitude and Whiterun.
Sneak behind the barkeeper and keep moving behind them against a wall. They will move a few times which mean you may have to move slightly each time they do.

You can get the Sneak skill to 100 in about 10 minutes very early in the game. I did it when following Hadvar not long after the beginning. You kill some mobs and then you get to a point where you can sneak around the bear. Hadvar tells you that he will follow your lead.

You can simply backtrack a little bit, wait for Hadvar to follow, then get behind him, crouch, and keep smacking him. You will level up your Sneak and One Hand simultaneously, though the One Hand is much slower. It took maybe 8-10 min to get my Sneak to 100, which took me to level 18!

http://i.imgur.com/QDA6MNw.gifv

Since it takes you to level 18, you will also pick up the level-based achievements for Apprentice (Level 5) and Adept (Level 10)!

Note: Since you will already be level 18 just starting the game, mobs will be around the same level as you, especially in dungeons. Basically, the hostile mobs level up with you in the game. I don't know if random bandits in the wild will level, but if you start the Bleak Falls Barrow quest at level 18 with low level weapons... gonna be tough! Your sneak will obviously be very high and you can execute a good amount, but it's not enough IMO.

I still had my level 1 weapons (I was able to upgrade just a tiny bit), but I had such a hard time just completing the first dungeon boss that I started a brand new game! Anyway, if you just want to unlock this cheevo quickly, you can follow my method and then start a brand new game to play the "normal" way.

Edit: I'm not sure why I have negative votes. It's a quick way to get to 100 lol

1) Get sent to Riften Jail. Escape, kill the two guards and grab your stuff from the chest. If you wish to raid the jail for more items to help, go for it.
2) Find Sibbi Black-Briar's cell.
3) Pickpocket everything you have onto him. Exclude your weapons for now since Sibbi may equip one and you won't be able to get it back at lower Pickpocket levels.
4) Pickpocket everything back. He (or the prisoner across the room) may notice you as you repeatedly push "Take" but nothing will happen.
5) Repeat steps 3 & 4 till you reach 100. Once you have obtained the Misdirection perk then you can add your weapons.

It seems tedious, but it works. Having The Thief Stone and any articles of clothing/jewelry with the Fortify Pickpocket enchantment help even more.