There are two kinds of sprites: "pure sprites", which are purely visual elements; and "unit sprites", which are sprites that act as units. Both sprites can be included with doodads, but standalone pure and unit sprites can only be placed using third-party map editors. Standard map editors limit mappers to placing 250 doodads with sprites. Third-party map editors allow an unlimited number of sprites to be placed, though StarCraft can only process 499 sprites in-game (including unit attack and death animations).
Because of StarCraft's limitations, it is wise to limit yourself to 450-490 sprites to avoid suppressing attack/death animations. Note that some units (such as Valkyries and Mutalisks) have very sprite-intensive attacks, and large skirmishes may require far more than 9 sprites.
Pure sprites are primarily used to enhance the feel of a scene. Sprites are always shown over terrain, and many are shown over units and buildings as well. This attribute is useful in that it allows mappers to do the following, among other things:
- Create a hiding spot.
- Enhance the look of a building or monument.
- Bridge a gap or disguise a flaw in extended terrain.
- Display an animation at the beginning of the game.
- Change or enhance the feel of an area.
- Change the look of a doodad.
More specific uses for particular sprites include:
- Using layers and groups of the Protoss Pylon Aura sprite to make an area look as though it were underwater.
- Using Hallucination death sprites at the bottom of an extended-terrain waterfall, to simulate splashing.
- Using Hallucination death sprites to simulate explosions.
- Using Disruption Web and Dark Swarm sprites to simulate fog.
- Placing Vespene Tank and similar extended powerups as decorative sprites, without having to worry about their hitboxes or about worker units picking them up.
Disabled unit sprites
Many unit sprites can be disabled when pre-placed, causing strange effects. Several sprites that incorporate tileset colors have two alternative modes that are toggled by disabling or enabling them, but most other sprites for units can do strange things when they are disabled. A complete reference can be found here.
Some unused and unidentified sprites can be placed on a map. Most of them will either animate once and disappear, or crash the game.
For example, "Unknown 06" will appear as an upward-moving blob of green smoke at the beginning of the map. When it's done animating, it will be invisible from then on. The "White Circle" sprites, on the other hand, all crash StarCraft when a map containing them is played.
Sprites and accuracy
It is commonly assumed that placing units under certain sprites makes it harder for enemy attacks to hit the units. This misconception results from the fact that units placed behind certain doodads (such as trees) are indeed harder to hit. However, it is the terrain of the doodad that causes this, not the sprite.
Sprites versus Doodads
Sprites are purely visual elements, and have no physical properties whatsoever. They are inert, and incapable of affecting anything in the map other than what players see. Doodads, on the other hand, are special pieces of terrain, and as such can affect unit pathing and vision. Doodads occasionally incorporate sprites, and some incorporate unit sprites as well.
Stackable unit sprites
For an easy look at how you would make sprites stackable, see: http://www.staredit.net/?file=270 The most stable units that can be used this way are:
- Terran Marine (and Jim Raynor (Marine))
- Terran Firebat (and Gui Montag)
- Terran Ghost (and Sarah Kerrigan, Samir Duran, and Alexei Stukov)
- Terran Civilian
- Zerg Zergling (and Devouring One)
- Protoss Dark Templar (and the hero variant)
Less stable units that can be used this way are: