Ghostly

• New mob: Infested Enderman
• Spawn rate of Infested Endermen is configurable; you can also enable/disable them
• Shades can infest Endermen, turning them to Infested Endermen
• Shades now spawn in the End, with the same rate as the Overworld by default.
• You can toggle Infested Endermen infesting other Endermen; doing so might be an ender pearl farming exploit.
• Shades have a special infest sound, as do Infested Endermen (their sound is lower pitched than a Shade's).
• Shades will disappear upon infesting an Enderman, due to killing it and then reviving it with their own life force. (This could be controversial, but oh well.)
• Infested Endermen do not spawn by default (their spawn rate is 0).
• Setting any mob's spawn rate to 0 will disable them naturally spawning. This was added in 1.0.3, I may have forgotten to put it into the changelog. Shades are an exception to this rule, however, having three different spawn rate values for the Overworld, Nether, and End.
• Possessed Swords actually use the spawn rate value in the configuration file (previously they only used it when checking that it didn't equal 0 to add the spawn in the first place)
• Infested Endermen take 2/3 of all damage applied to them (with some exceptions), and fall 2/3 as fast as a normal entity would. However, they are not immune to explosions, thrown damage, magic damage, and fire damage like Shades are. They will take only 1/3 of that damage, though.
• Shades can also be configured to infest Endermen, by default they don't

Warning: Infested Endermen may be buggy.