Essence Drop

In some Action Games, after you kill enemies, they will release magical spheres of some sort that affect your character's status in some way when you collect them -- they may represent Experience Points, health or Mana refills, and so on.

Whatever exactly these things are is rarely addressed; sometimes it's handwaved as the opponent's soul/blood or a more vague "essence".

The exact number, types and effects of these things will vary with each game, and may or may not also be found stored in inanimate objects.

A Sub Trope of Random Drop. See also Money Spider and Organ Drops.

Action Adventure:

 * In American McGee's Alice, dead enemies disappear after killed to leave for a while some "metaessence", that comes in differents shapes (spheres, hearts...) but allow to regain health and mana.
 * Used to some extent in the Soul Reaver series: Raziel has to suck up dead enemies' souls to refill his health. In 2 and Defiance, the souls' shape and colour differs depending on if you kill a human or a demon, although the effect is the same.
 * The Amana Volo spheres in Bionicle replenish your stamina meter, which lets you use some of the special items you can find, like Onewa's rock-crushing hammer.
 * Enemies in Bunny Must Die will drop Time Crystals when Bunny kills them, refilling her time meter.
 * In Metroid Fusion, slain enemies drop X-Parasites. Samus is half-Metroid in this game so she can feed on X-parasites like them: yellow is energy, green is ammo, red restores both, so on. And for boss/midboss level parasites, you also get back one of your weapons/abilities.

Action RPG:

 * Games in the Kingdom Hearts series have several types of these spheres, depending on the game.
 * Green Orbs are HP
 * Blue Bubbles are MP
 * Yellow Orbs are Munny
 * Red Orbs are Moogle Points (In Kingdom Hearts Chain of Memories)
 * Orange Orbs are for the Drive Gauge (In Kingdom Hearts II)
 * Blue, Star-like Orbs refill D-Link (In Kingdom Hearts Birth By Sleep)
 * Otto Matic has virtually everything you kill drop "atoms" in different colors... red restores health, green powers your "jump jet" and blue is "rocket fuel" needed to finish the level. Not sure if this counts though because it is never indicated to be part of their souls.
 * Somewhat more ickily, there are Slimes on planet Snoth that you can freeze with an Freeze Gun and then shatter by punching them. For a while thereafter they become a mass of little balls that you can pick up to gain one of the things mentioned above, depending on the color of the Slime. Of course, if you don't pick up all of them, any that remain turn into more Slimes.
 * In Odin Sphere enemies release floating "Phozons" when defeated, which are said to be the remnants of their life force. It is used mainly to level-grind your weapons.

Fighting Game:

 * In Tatsunoko vs. Capcom, Soki from Onimusha: Dawn of Dreams assumes his Black Oni form for his Level 3. During this time, his partner is unavailable and his hyper meter begins to dwindle. Attacking his opponent will cause multicolored soul orbs to pop out, which Soki needs to collect using the Partner button. The blue and yellow orbs respectively restore Soki's hyper meter and health, but the red orbs are the most important, as collecting seven or more of those orbs gives Soki access to his strongest Hyper, Oni Cutter.
 * Naruto Shippuden Ultimate Ninja Storm 2 allows you to absorb blue spheres that fall from your opponent after a strong hit, to refill your Chakra gage more quickly.

First Person Shooter:

 * In Painkiller, every enemy you kill drops a soul. Regular enemies drop green souls which heal one HP, while Elite Mooks drop red souls which heal 6 HP. After collecting 66 souls (either color), you enter a berserk Demon Morph mode.

Hack and Slash:

 * Devil May Cry is maybe the Trope Codifier for modern action games, with the crystallised demon blood that enemies (and chairs) drop: red orbs are the currency, green orbs heal you and white orbs refill your Devil Trigger gauge.
 * In the modern Ninja Gaiden games, dead enemies drop yellow orbs (currency), blue orbs (health) and red orbs (Ninpo gauge). Also, instead of using them to heal, you can absorb them to charge an ultimate technique instantly; that's actually a vital skill when facing multiple enemies in 2. Ninja Gaiden 3 abandons this system completely for the sake of a greater immersion.
 * In God of War, monsters drop red, green and blue orbs, for experience, health and magic respectively.
 * Dantes Inferno is very similar to God of War in many ways; it uses colored "souls" to keep track of experience, health, and mana.
 * Onimusha subverts this system: enemies drop soul spheres, but you have to stop and attract them to you manually, which takes a bit of time and is very risky in the middle of a fight (the bigger the spheres are, the longer it takes). The game also adds a fourth type of (very rare) sphere, and collecting five of these allows you to transform into an Onimusha.
 * Diablo III features this: Dead enemies occasionally drop "life orbs", which allow to regain some health. This is meant to do away with previous installments' (and much of the genre's in general) need to constantly swig health potions, making said potions more of an emergency healing option (which now have a cooldown attached).
 * While enemies in Bayonetta are mostly Money Spiders, sometimes they also drop small green, leaf-shaped or purple, butterfly-shaped things that refill a bit of health or magic.

Platform Game:

 * In the night stages of Sonic Unleashed, any defeated enemies give out pale bluish floating bits of light. Sonic could collect these to fill up his Unleashed gauge, which when activated by the player, temporarily gives Sonic increased attack power and invincibility to some things. In the Wii and Play Station 2 versions, enemies also give out red floating bits of light which represents experience points.
 * The Nightmare Souls on Mega Man X6 can be considered something like experience points. After certain amounts are accumulated they increase by one the limit of special power-ups you can use.
 * In Flink, defeating enemies would release magical energy that would home in on Flink and be absorbed into his Life Meter. Magical energy would also be released if Flink took a hit, allowing for damage recovery similar to rings in Sonic the Hedgehog games.
 * Jak and Daxter The Precursor Legacy: enemies drop green Eco on death, and collecting 50 green Eco restores a quarter of your health. This was dropped in all subsequent games.

Role Playing Game:

 * Enemies in Minecraft drop flashing green-and-yellow experience orbs upon death.

Web Games:

 * Indestruc2Tank Enhanced Game mode. When you destroy an enemy vehicle, little globes of white light come out of it and drift towards your tank. When they touch your tank, your Boom Bar is increased.

Wide Open Sandbox:

 * Prototype does this for most enemies. Some are more rewarding towards vitality, some towards Evolution Points. The sequel does away with this mechanic entirely.

Miscellaneous Games:

 * In Attack of the Mutant Penguins, penguins will drop a bunch of power orbs if you hit them without killing them. Collecting these orbs before swinging your weapon again will power it up to be lethal to penguins.

Non-video game example:
 * Puella Magi Madoka Magica: Some witches drop grief seeds after their defeat, which cleanses a magical girl's soul gem and refills her magic.