Dark Side prestige classes for a [Lawful, Good] character.

[Chambers]

I've been tinkering with a character concept for my own amusement lately and would like some help. The idea is pretty simply, a Trumpet Archon (http://www.d20srd.org/srd/monsters/archon.htm#trumpetArchon) who has taken up the methods of less savory characters in order to bring about justice. This character is Gestalt and for the purpose of this thread is a level 30 character.

Some ideas to get the ball rolling.

Grey Guard.
Malconvoker.
Dread Witch. Need to get Scare on the Cleric spell list.
Nar Demonbinder.

[Occasional Sage]

Perhaps make some tweaks or refluffs to Pathfinder's Low Templar (http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/i-m/low-templar)? It's a PrC for Han Solo types on a crusade against an Abyssal portal: you get the mercenary shifting loyalties and eventual redemption (or downfall I suppose), with a nice mix of Rogue and Fighter feel: move-action Withdraws to hit and move, some SA progression, bonuses to attacks, damage, and Will saves vs CE outsiders, status effects from crits, and masking your alignment from effects targeting you ("Save-or-suck if I'm Good? Oh no, not me, I'm certainly not Good!") are the highlights.

[Chambers]

Perhaps make some tweaks or refluffs to Pathfinder's Low Templar (http://www.d20pfsrd.com/classes/prestige-classes/other-paizo/i-m/low-templar)? It's a PrC for Han Solo types on a crusade against an Abyssal portal: you get the mercenary shifting loyalties and eventual redemption (or downfall I suppose), with a nice mix of Rogue and Fighter feel: move-action Withdraws to hit and move, some SA progression, bonuses to attacks, damage, and Will saves vs CE outsiders, status effects from crits, and masking your alignment from effects targeting you ("Save-or-suck if I'm Good? Oh no, not me, I'm certainly not Good!") are the highlights.

The alignment masking with Path of Darkness/Path of Light and Damnation/Redemption abilities seem like a good fit, but I'm not that impressed with the rest of the prestige class. Know of any similar 3.5 prestige classes that have a similar ability?

[Sith_Happens]

Bone Knight is a paladin-friendly undead-themed prestige class, so probably a perfect fit for this character.

[Occasional Sage]

The alignment masking with Path of Darkness/Path of Light and Damnation/Redemption abilities seem like a good fit, but I'm not that impressed with the rest of the prestige class. Know of any similar 3.5 prestige classes that have a similar ability?

Yeah, it's not a stellar class. "Withdraw as a Move" being a high point sets the bar at... pretty middling.

I don't think I've seen anything like it in 3.5; if I have, my old-man memory has lost track of it.