Bukkit/Bukkit — pull request #381 by amaranth (2011-10-13 23:49:20+00:00)
Title: add EntityTrackEvent and Entity.setInvisible and Entity.isInvisible

This allows plugins to mark entities as invisible and hides them completely (no further packets sent about them).

A plugin can also handle the ENTITY_TRACK event to setup custom rules for what players can see what invisible entities.