Large amounts of Green Gel are consumed to enable Sebastian Castellanos to upgrade his gear and abilities.
Green Gel is a seemingly viscous, fluorescent green fluid stored in glass jars that are secreted by the many creatures inhabiting STEM spaces when they die. When exposed to air and not contained in a sealed jar, the Gel would appear to bubble and slowly evaporate, though it loses much of this perceived volatility when collected.
Nearly all enemies in the games drop Green Gel when slain, and the larger and more challenging the enemy, the more Gel will usually drop. Playing on New Game+ will in most cases cause enemies to drop more Green Gel than usual.
Red Gel is a new subtype appearing in The Evil Within 2. Unlike Green Gel that can be found in vast quantities throughout the game, Red Gel vials only show up every now and then, and are collected in units of one at a time. As rare as they are, Red Gels are fortunately only spent in single vials to unlock additional skill paths in the upgrades screen.
Green Gel acts as a form of currency, used for enhancing skills and equipment at the Safe Haven.
By the time of The Evil Within 2, Green Gel is no longer used to enhance Sebastian's arsenal. Such is the purpose of Weapon Crafting parts instead.
- While the sound effects of Sebastian harvesting Green Gel might imply that he simply scoops up the fluid with a jar, the actual animation involves him drawing the gel up with a Syringe.
- The depicted use of Green Gel implies that the compound is some sort of psychosomatic fluid that are applied directly to the patient's brain to improve their many higher functions.
- Seeing as STEM operates by interfacing directly with the human mind, the results of upgrading Sebastian's many abilities could be interpreted as him using the Gel to strengthen this mental connection, thus granting him more perceived power within its worlds.