Kingdoms of Amalur: Reckoning

To backstab an enemy, you either need to have a pair of daggers or faeblades equipped in either weapon slot. Then essentially all you have to do is sneak up on 20 enemies and backstab them for the achievement.

I found a great spot to grind this out was in the forests north of Gorhart. Enemies appear as arrows on your mini map, you can use this to help you sneak up behind them. I also leveled my daggers up a bit so that I could quick kill enemies in one shot (you will know this is possible as when the X appears to backstab an enemy, if the X glows Red in color you will kill the enemy with the backstab).

I also had 3 points in my Stealth ability which helps a lot. Watch the icons above your enemies heads as this will help you indicate when they are close to detecting you. If you sneak up on an enemy and another sees you, you can quickly roll out of the area and usually (not always) they will leave you alone after a few seconds. Rinse and repeat til the achievement pops.

A helpful note from user Soulflare: Enemy locations as arrows only appear if you have invested 3 skill points into the Detect Hidden skill. It requires 1 point applied into Detect Hidden to even see enemies positions at all.

A minor note courtesy of user Saber LoneWolf: You do need at least 1 point in the Finesse skill called Assassin's Art to have the ability to backstab. Please note that all new characters are automatically given a point in this skill making it possible for any character to backstab as soon as they receive a pair of daggers.

Basically any humanoid enemy counts for this. One important thing that I've found helps is that you can repeatedly combat roll while sneaking (B button) and it will help you sneak up to something quickly while remaining undetected. Side note for people who perhaps didn't pay attention to the tutorial, sneak is RB button and backstab is whatever button you mapped daggers to, and when you are within range you tap the corresponding button.

Finding this out I was easily able to clear 20 as a Soldier with no investment in the Sneak skill. If you're used to the usual stealth methods in other games, mainly staying behind targets and out of sight when you don't have an opening, this will be easy regardless of class.

As far as places I'd recommend, that even benefit from this method, I would say Lorca-Rane is the best spot for this. It easily has a dozen Jottun that respawn every time you return, and divide and conquer is almost necessary on them to prevent wasting potions fighting them all at once. These guys are ideal because most of them sit in one spot and don't patrol or turn around, as well as the fact that Jottun generally don't bunch up together, they stay spread out.

After all the frustrations with getting bashed into the ground by three Jottun on Hard difficulty, I was satisfied to find I could sneak up and eviscerate their throat with little effort.

The achievement is unlocked when you backstab your 20th enemy. If you execute a stealth kill in the manner in which it is taught in the prologue, you will have performed a successful backstab. Equip the daggers in either primary or secondary weapon slot. Approach an enemy in the crouched position (dodge-rolls and the dodge-teleport of some higher level destinies performed when in the crouched position retain you in the crouched position). Press the button when you see the prompt ( if the daggers are primary - if they are secondary). You will know when you have performed a proper backstab when the kill is accompanied by an animated sequence. If in doubt, activate the achievement tracker and make sure it advances on your stealth kills.

This may be performed by any vocation at a low level. The introductory character in the prologue is able to perform a backstab. However, you must inflict enough damage to instantaneously defeat the character. So, increased levels, more powerful daggers, and investment in the finesse Assassin's Art ability all contribute to the lethality of your sneak attacks and increase the enemies that can be backstabbed.

Some enemies are most easily defeated with a backstab. Accordingly, I recommend obtaining this achievement in normal play rather than grinding it out. The below video (made on Re-Reckoning) shows the achievement unlocking in The Natural Order quest where you must kill ten Jottun. They are powerful, have tough skins, and resist normal attacks. Yet, they are vulnerable to the backstab. Why engage in a prolonged fight when you can get a quick kill? Where you cannot sneak up on them, you can get them to run after you. When they lose interest and turn around, you can sneak behind them using roll-dodge to catch up to them, and backstab them when the prompt appears. I like to equip the daggers as the secondary weapon because then I can perform a backstab whenever the situation presents itself without opening up the inventory menu to change weapons.