I'd even though a little about faint, so moderate is good with me.
How about the trilloch's rage upthread?
Control Rage (Sp): A trilloch can inspire rage (as a rage spell, but with a DC 18 Will save allowed to negate the effect) in all living creatures within 180 feet at will. Each creature gains a +4 morale bonus to Strength and Constitution, a +2 morale bonus on Will saves, and a -4 penalty to AC. This effect is otherwise identical to a barbarian's rage ability, except that the subjects aren't fatigued at the end of the rage. If a creature has the rage ability and its bonuses when raging are greater than those given here, it can use the other bonuses instead. The save DC is Charisma-based. This is a mind-affecting compulsion effect.
An affected creature can end its rage by making a DC 19 Will save. The trilloch can end the rage for any number of creatures prematurely, without affecting other raging creatures. It can also end a rage caused by any other effect, such as a barbarian's rage ability, and in that case the barbarian would become fatigued. A trilloch always ends the rage for a creature who has gone beyond its normal hit points and into those granted by the rage, likely killing it.
This effect lasts for as long as the trilloch concentrates on it, plus 1 round per Hit Die of the creature.
The death shade absorbs 1 energy level for every hit die of an opponent killed within a 10' radius, and can store up to 40 energy levels at one time.
The death shade and its host become catatonic when stored energy levels are at zero. The host and shade may remain catatonic for as many days as the host has Con points; after that, both host and shade die. If a lifeform comes within 10 feet of a catatonic host, the death shade rouses the host in 1d3 rounds in a berserk rage to kill the creature for its energy. After the rage subsides, the host must make a save vs. paralyzation or have permanent brain damage (subtract 1d3 points from the host's Intelligence).
Death shades reproduce as a by-product of feeding. After a death shade has absorbed life force from the death of 40 hit dice or levels of creatures within a 24-hour period, it splits into two death shades with 20 energy levels each. The second shade immediately transfers to any creature within 20'. If it can't make the transfer within 5 rounds, the second death shade dies.
Death shades have a basic telepathy which can only identify the presence of one death shade to another. Thus, death shades can detect each other's presence in a 20 foot radius and, if given a choice of targets during "feeding," will attack an uninfested creature before an infested host body.
How do we want to handle these "energy levels"? Give it something akin to energy drain, but only usable upon a dying creature? Some combination of death knell and energy drain?
Do we need an ability writeup for this, or will flavor text suffice?
Once again, an ability or simplify like so? "Death shades cannot speak, but can communicate telepathically with one another."
I'd make it like death knell, but granting the death shade something like a positive level (but without benefits?). Or introduce a new "counter" for them. This is similar to what we did for blood warriors (I think) and the transient golem.
Probably flavor on the reproduction, though I wouldn't mind an ability. Definitely put the telepathy in the language line like that.