Doomed has a lot of weird or quirky talents that have odd interactions with other talents and prodigies, so I figured that I'd start a list documenting the various quirks as reference for those who want to explore different builds and synergies.
Punishments:-None of the spells in the tree can proc on-mindpower hit effects as far as I can tell. Using the Crimson Robe over a few hundred turns, I was unable to get either Reproach, Agony, or Hateful Whisper to trigger the robe's innate Agony and Hateful Whisper procs. I am unsure of why this is.
-Madness is pretty straightforward in how it works, but keep in mind that in order for the effects to trigger the damage has to come from you - i.e. Force of Will, Darkness, Punishments, and Fears (Haunted effect) will all cause it to proc. Cursed Bolt will NOT trigger any of its effects, as the bolts are considered to come from the shadows themselves.
One with Shadows:-Shadow Empathy is considered a magical effect, so it can be extended by Timeless. Furthermore, the damage it causes to shadows is blocked by Fade, so if even a single shadow has the effect you can be confident that the damage deflection will work. I have yet to find out whether shadows can use Reform to resurrect after dying to this deflected damage but I'm inclined to say they will.
-Shadow Transposition seems to have a chance to clear the status entirely from both you and your shadow when used. Multiple times I have used to to clear a nasty disease or poison only to notice that the transposed shadow does not have the effect. If anyone can figure why this happens let me know.
-According to
http://forums.te4.org/viewtopic.php?f=58&t=40264, Shadow Decoy will trigger before cauterize. Make of that as you may.
Advanced Shadowmancy:-Because all of the talents use the shadows themselves as the sources of damage, none of the spells will a) trigger on-mindpower hit procs, b) be affected by damage conversion sources (Mental Tyranny, Elemental Fury, Temporal Form, etc.), and c) proc Madness (in the case of Cursed Bolt). However, they do seem to benefit from +damage%, respen%, crit chance%, and crit mult%, and will cause hate or psi on mind crit effects to trigger.
-Zemekky's Hourglass can be used to great effect with this tree as shadows ignore the damage penalty you have; this can be used either for free damage or with Shadow's Path and Shadow Transposition for a perfectly accurate long-range teleport.
-Merge, Stone, and Cursed Bolt use an enemy's range from the shadow to determine if they can hit or not. The first two talents require direct LoS from you to your shadow for targetting, so even with Shadow Senses you cannot choose a shadow behind a wall. Shadow's Path and Cursed Bolt do not require LoS.
Fears:-Fears are pretty straightforward, though of note is the fact that the Haunted effect's mind damage can trigger Madness.
Gestures:-This post
http://forums.te4.org/viewtopic.php?f=61&t=38628&start=15#p172243, though meant for Adventurer talent interactions, describes a lot of how the Gestures attack works, though there are a few other quirks. Gestures cannot trigger on-mindpower hit effects, and because it does NOT use a weapon attack most on-hit effects will not trigger. Flexible Combat will cause an additional Gesture attack, but even when unarmed the glove/gauntlet effects will not occur.
Cursed Aura:-Weapons used as Cursed Sentries will attempt to use activated effects on weapons, meaning projection weapons, blasting staffs, and hungering mindstars, for example, will use their ranged attacks (To be tested: whether fungal bows or slings use the regen effect). Furthermore, ranged weapons chosen by Cursed Sentry will spawn with ammunition equivalent to the tier level of the weapon used, and can generate egos for this ammunition - whether greater egos can spawn is yet to be tested. On-hit effects will trigger and will likely do so given the high global speed of the sentry.
Let me know if there's any important talent interaction that's missing or that should be included in this list.