Outward

Note: This skill will destroy your lantern every time you use it.

Edit: According to a recent comment, a patch has made this achievement unobtainable. The devs are looking into it.

2nd Edit: According to recent comments, this achievement is obtainable again, however, Jennitiger1138 noted that the achievement track will not update until you throw the lantern all 5 times.

You can assign the throw lantern to a quick slot from the menu. Assign it wherever you wish, then make sure you have 5 lanterns total. As stated above, each lantern will be destroyed after you throw it, so it's wise to use cheap, low-quality ones for this skill. You can occasionally find lanterns when exploring. But the general goods merchant in Cierzo will also have a few to sell as well.

When you have enough lanterns, make sure the skill is assigned. Then, place one lantern in your hand. You do this from the inventory screen. Once your character is holding one, hold down + whatever button you mapped the skill to. This will throw the lantern, lighting a small area on fire.

From there, just assign the next lantern and throw. This does not need to be in combat. I threw all 5 of mine in Cierzo to earn the achievement. Alternatively, you avoid buying all the lanterns by just using the skill when you have a lantern to spare. It's really up to you.

After the 5th throw, the achievement will pop.