These enemies would be immobile Tower-like structures about the height of a Trojan that have various effects on those nearby. They would have lots of health to make up for not being able to move or attack, and higher tier ones can spawn orbiting shields similar to those of the Battlepod to defend themselves. The two types of Pylon would be:
a) The Construct Pylons, which would Buff nearby Enemies.
b) The Fiend Pylons, which would Debuff nearby Knights.
And each Pylon generates one of the following effects (Construct Buff/Fiend Debuff):
1) Strength/Weakness (increases/decreases damage. Appears in all tiers)
2) Sturdiness/Fragility (decreases/increases damage taken. Appears in all tiers)
3) Speed/Slowness (increases/decreases speed. Not as powerful as the other effects. Tier 2 and 3 only)
4) Luck/Misfortune (increases/decreases chance of Status Effects occurring on hit. Tier 2 and 3 only)
5a) Life (Construct) (Has a small chance of reviving nearby enemies. Tier 3 only and more fragile than a normal Pylon.)
5b) Death (Fiend) (Knights who die near this Pylon cannot revive until the Pylon in question is destroyed. Tier 3 only and more fragile than a normal Pylon.)
5b alt) Death (Fiend) Alternative (Knights who revive near this pylon have half the health they would normally have. For example a Knight who revives using CE near this Pylon revives with 50% health instead of 100%.)
6a) Might (Construct) (Makes one monster in the AoE invulnerable, this effect lasts until the Pylon is dead or the Monster moves too far from the Pylon whereupon it targets another monster in the AoE. Tier 3 Only)
6b) Helplessness (Fiend) (Makes one Knight in the AoE do greatly reduced damage to everything but the Pylon in question, this effect lasts until the Pylon is dead or the Knight moves too far from the Pylon whereupon it targets another Knight in the AoE Tier 3 Only)
7a) Accelerator Pylon (Construct) (Increases Attack Speed of nearby Enemies. Appears in all Tiers. Suggested by Kentard)
7b) Decelerator Pylon (Fiend) (Increases Charge Time of nearby Knights. Appears in all Tiers. Suggested by Kentard)
All Pylons are immune to Stun and Curse since they don't move or attack. Their effects do not stack with other Pylons of the same kind (so an enemy in the area of two Strength pylons only gets the bonus from one.), with the exception of the Life Pylon.
8) Clumsiness (Fiend) (Items cannot be used while in this Pylons AoE. Tier 2 and 3 only)
Concept art (courtesy of Kentard):
http://img29.imageshack.us/img29/6024/pylonv.jpg
Yeesh, Death sounds dangerous to soloers, especially since, because it's Fiend based, it comes with Devilites and/or Greavers (solo bomber's nightmare). By revive you mean both via HP and via CE I assume. Good.
Maybe a danger room with pylons could be a nice challenge.