code/game/objects/effects/effects.dm 
| /obj/effect/abstract | This is an object that is intended to able to be placed, but that is completely invisible. The object should be immune to all forms of damage, or things that can delete it, such as the singularity, or explosions. |
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| /obj/effect/abstract/particle_holder | These effects can be added to anything to hold particles, which is useful because Byond only allows a single particle per atom |