Okay, back to Flipguarder at the top of the list, and thoughts:
I'm just not sure about Illurien or treants. There's probably a way to do treants that is cool; I just haven't come around to it yet. For Illurien, I'd suggest maybe poaching some of the deva feats (or upcoming gith* feats and reskinning them as prophetic/knowledge-based rather than psychic or radiant, and attaching them to watersoul genasi. Keep the watersoul feats as well, and don't permit and of the extra manifestation-type feats. Done.
Ghosts follow. Bobdud, I might point out that these are built specifically to be cool for rogues (particularly if they're splashing in some necrotic effects somehow)
Ghost
Dead men tell no tales—or do they?
Ability Score: +2 Dex, +2 Cha
Size: Medium
Speed: 6
Vision: Normal
Languages: Special
Skill Bonuses: +2 Intimidate, +2 Stealth
Undead Origin: Ghosts are the semi-corporeal remnants of living beings; as such, you are considered an undead creature for the purpose of effects that relate to creature origin.
Past Life: Select a race without the undead origin. For the purposes of the prerequisites of feats, paragon paths, and epic destinies, you are a member of the selected race. (This is just a revised version of the revenant's ability, taking into account the possibility of multiple undead races.) Furthermore, you receive languages as though you were a member of the selected race.
Ever-Living Ghost Body: You have a +5 bonus to saving throws against poison and disease effects.
Eyes of the Dead: If a creature adjacent to you takes necrotic damage, it grants combat advantage to you until the start of its next turn.
Choose a subtype:
Possessor Spirit
Subtle Possession: You have the subtle possession racial power.
Subtle Possession — Ghost Racial Power
You skein your soul into the body of your enemy, hindering him.
Encounter ♦ Charm, Fear
Standard Action, Ranged 5
Target:One creature
Attack: Cha +2 vs. Will
Increase to Cha +4 at 11th level and Cha +6 at 21st level.
Hit: The target is dazed and you are insubstantial (target's save ends both).
11th level: The target has a -2 penalty to his save.
21st level: The target has a -4 penalty to his save.
Special: If you move more than Wisdom modifier +3 (minimum 3) squares from the target, the effect ends.
Vengeful Spirit
Wailing Spirit: You have the wailing spirit racial power.
Wailing Spirit — Ghost Racial Power
You release an unearthly wail.
Encounter ♦ Psychic
Standard Action, Ranged 10
Target:One creature
Attack: Cha +2 vs. Will
Hit: 1d6 psychic damage and push the target one square.
Increase to +4 and 2d6 damage at 11th level and +6 bonus and 3d6 damage at 21st level.
Physical Description
A ghost is the spirit of a dead creature. Their form is altered indelibly by the manner of their deaths: while those who died peacefully are often luminous, misty figures with subtle and calm expressions, those who died by violence sometimes carry their wounds for many years.
Universally, ghosts have long hair that drifts as though underwater, and in the dark wells of their eye sockets are dancing blue sparks. Even when their eyes are shut, they can be seen twinkling between their eyelids.
Feats
Heroic Feats
Poltergeist
Prerequisite: Ghost
You gain the at-will cantrips mage hand and ghost sound.
Funereal Privilege
Prerequisite: Eyes of the Dead
You gain the benefit of Eyes of the Dead whenever a creature adjacent to you uses a power with the necrotic keyword.
Lasting Privilege
Prerequisites: Eyes of the Dead, Funereal Privilege
The duration of the effect of Eyes of the Dead is changed to 'save ends.'
Distant Shroud Vision
Prerequisites: Wis 13, Eyes of the Dead
You can gain the benefit of Eyes of the Dead against creatures up to 5 squares distant, instead of adjacent to you.
Diaphanous Ghost
Prerequisite: Subtle Possession
You have concealment when you are insubstantial.
Distant Possession
Prerequisites: Int 13, Subtle Possession
You may move any distance from the target without ending your subtle possession.
Wracked Possession
Prerequisites: Cha 13, Subtle Possession
Your subtle possession has ongoing damage: 5 necrotic.
Bewildering Wail
Prerequisite: Wailing Spirit
When your wailing spirit hits, slide the target instead of pushing it.
Paragon Feats
Subtle Possession
Prerequisites: 11th level, Ghost, Vengeful Spirit
You can use subtle possession as an encounter power.
Wailing Spirit
Prerequisite: 11th level, Ghost, Possessor Spirit
You can use wailing spirit as an encounter power.
Hair-Raising Wail
Prerequisites: 11th level, Ghost, Wailing Spirit
When your wailing spirit hits, move the target Cha modifier squares instead of one.
Piercing Ghost Eyes
Prerequisites: 11th level, Eyes of the Dead, Distant Shroud Vision
When you gain combat advantage against a creature due to Eyes of the Dead, you also ignore its concealment.
Grand Possession
Prerequisites: 11th level, Subtle Possession
Creatures affected by your subtle possession are dominated by you.
Torturous Possession
Prerequisites: 11th level, Subtle Possession, Wracked Possession
Your subtle possession has ongoing damage: 10 necrotic (this replaces the benefit of Wracked Possession) and aftereffect: ongoing damage 5 necrotic (save ends).
I hope I've made these guys nasty enough without making them, um, broken. I'm pretty excited by the possession feats especially.