env_warpball
env_warpball is a point entity available in all 
GoldSrc games. It was added in the Dreamcast and Playstation 2 ports of Half-Life. It is used in 
Half-Life: Decay and 
Half-Life: Blue Shift. Even the PC version of Blue Shift uses this.
env_warpball is the warp-in effect when aliens from Xen teleport into a location. It can be seen in Half-Life and its expansions. It was first named in the Dreamcast version of Half-Life: Blue Shift.
In 
Half-Life and 
Half-Life: Opposing Force, the warpball effect is a combination of entities producing sprites, beams, and sound effects. It appears as a small flashing transparent green ball that emits green light with energy beams projecting out of it. This method was replaced in the Dreamcast port of Half-Life with env_warpball, a single entity which handles the effect's creation. This allowed for easier placements of the effect in the maps by level designers. They can be obstructed to prevent the enemies from teleporting in. In Blue Shift and later installments, warpballs damage the player when in close proximity. This was most likely added to discourage the player from blocking them.
Key Values
- Target (target) <targetname>
- The targetname of an entity this entity will trigger when activated.
Targetname:
- Name (targetname) <string>
- The targetname that other entities refer to this entity by.
- Warp Target ([todo internal name (i)]) <target_source|targetname|target_source>
- The targetname of an entity this entity will trigger when activated.
Flags
- 1 : Remove On fire
- Remove this entity after first use.
- 2 : Kill Center
- Kill anyone who is in the way?