Fun with testing:
The bonus damage taken while under the effects of banishment/Mask of Madness is reflected with Blade Mail, as it returns damage calculated after modifiers.
Mask of Madness works as expected with Spectre's Dispersal, meaning that the extra damage is properly calculated into reflected damage.
The combination of Blade Mail and Dispersal means that anyone hitting Spectre during that time period will actually do MORE damage to themselves than to her.
Desolate is, as expected, not counted into lifesteal. Neither with modifier-lifesteals nor aura-lifesteals.
Spectre cannot realize into Manta illusions, but they do of course carry Desolate as standard haunts do.
Razor's illusions carry his full passive, with purging, slowing, damage and all. Axe's illusions can counter helix, and damage is not reduced for these.
Refresher orb can "stack" a few interesting things, such as Razor's Eye of the Storm and Spectre's Haunt (does not work with Manta though). You can't stack Necronomicon summons from the same book, but you CAN do it from two different books. Use one, refresh, then use the other. Using the same book will overwrite the spawns.
As you can probably tell, I've found the debugging commands.