Incendiary Grenade

The incendiary grenade is an improvised incendiary device that was created from scrap by the Moscow Metro dwellers at some point after the Great War of 2013. It appears in Metro: Last Light and both Metro Redux games.

Overview
In Metro: Last Light and Metro Redux, the incendiary grenade replaces the sticky grenade appearing in Metro 2033. As the name suggests, the incendiary grenade is a thrown explosive that shatters on impact with any surface, including enemies. It explodes in a ball of flame and ignites the nearby area for a few seconds. Although lethal to any human caught in the blast, mutants are especially vulnerable, as they will rarely avoid the flames to get to Artyom.

Incendiary grenades can be used to ignite enemies, which will cause them to flail around in pain for a few seconds before dying, or to block off narrow passages; throwing lots of these grenades at the same spot increases the radius of the lingering flames. Plus, because the flames produce light, you can use these to keep spiderbugs from reaching you. Conversely, human enemies will spot the flames and be alerted to your location. But bear in mind that the flames will go out in just a few seconds, so a fully charged flashlight will work better at keeping spiderbugs away. Also, large mutants may not be affected as much by this gadget as their smaller counterparts, like the demon, bear, and rhino. However, once on fire, they are generally vulnerable to attack.

Incendiary grenades were added to Metro 2033 Redux. They are useful against multiple mutants encountered in the later portion of the game. Because Metro 2033 has a lot of indoor combat, it's somewhat useful against human enemies around the corner or to keep them from reaching your location.

In Metro Exodus, a very similar thrown weapon, the molotov cocktail, appears. It works in the same way as the incendiary grenade - the main differences are purely cosmetic.

Aquisition
Incendiary grenades can be bought from weapon vendors; one grenade costs 15 MGR to buy. They can also be found in the game world, albeit they are rarer than regular frag grenades.

Trivia

 * Based on the yellow glow of the liquid inside the incendiary grenade, the primary incendiary agent may involve the use of a highly reactive acid. It may also incorporate a common accelerant, such as gasoline or alcohol, to prolong the burning.
 * It's unknown what incendiary grenades are made from; possibly repurposed fluorescent light tubes, sealed at both ends, with a manually ignited fuse.
 * Incendiary grenades are notably very effective against shrimps, possibly due to shrimp generally living in wet conditions; they simply cannot tolerate that much heat. They also shine when used for making a wall of fire to fend off nosalises. This is particularly useful at the end of the "Bandits" level, where facing the horde of nosalises alone can be quite a challenge.
 * Incendiary grenades have a natural glow due to the yellow liquid inside being visible through the clear glass, making them easy to spot in the darkness of the Metro, or on the surface at night.