Etherealness is a trait that indicates some incorporeality. They might have a Spiritform, like a Ghost, or they might only barely exist in this world (like, according to the lore, a Shadow Seer). The trait functions a bit like "Blink" from Dungeons & Dragons.

If a hit isn't magical, it has only a 25% chance (at most) to actually do damage; the Damage and Protection rolls aren't even taken, unless the 25% chance works. The hit still lands, though, so "on hit" effects (that are magical) still apply. Why isn't the chance zero? Because if it were zero, that would indicate that the fellow isn't able to interact with our world at all. Magical hits have that little white star next to their damage values, while non-magical hits from spells typically specify that they're nonmagical.

Aside from most weapons, what does Etherealness help you avoid?

• Trample damage, including the minimum 1 point if you'd succeed
• Repel damage
• Bleeding (from nonmagical hits, since their blood and blood vessels are incorporeal)
• Burning (100% protection, since regular fire has to burn present things)
• Freezing (100% protection, since only present things can be frozen)
• Most methods of Entrapment (and the Ethereal fellow can slip out from most with ease)
• Various spells, such as Blade Wind, Earthquake, Rain of Stones, Gust of Winds, Storm Winds, and so on
• The partial liquifying effect of a failed Liquify – this is nonmagical, for some reason

Oh, and Ethereal fellows can also walk through walls. They're worse at Trampling, however, dealing halved damage.

All Spiritforms are Ethereal, but not all Ethereal fellows are Spiritforms. Spiritforms are especially incorporeal; not merely phasing out of reality in most instances, these fellows have to try rather hard to be coherent enough to land a hit. They cannot be made real, so:

• They can't be petrified
• They don't have bones to melt with Bone Melter - This means they're 100% immune, instead of just 75% like regular Ethereals
  • They also can't be turned into goo with Liquify
• They can't be Transformed into anything, really, so Polymorph and Curse of the Frog Prince don't work
  • They also can't benefit from the Twiceborn and Lichcraft Enchantments, however
• They can't enjoy the following Alterations:
  • Protection-boosters, such as Barkskin, Stoneskin, or Ironskin (all of which require real skin)
  • Mossbody (since that requires real skin)
  • Liquid Body (since they're not solids that can be made fluid)
  • Stygian Skin (since that requires real skin – Stygian Rains works for some reason, though)
  • Skeletal Body (since that requires real bones – Skeletal Legion works, though, making them incorporeal bones or something)
  • Enlarge (and Shrink, but Shrink is an enemy spell – their Size has little-to-no bearing on their abilities)

Illusions are very similar to Spiritforms, being unreal constructions of light. They have an additional weakness, however, in that they can be disbelieved. These fellows are largely the same as the old Phantasms from Dominions 5, with 1 HP, Lifelessness, and vacancy; in Dominions 6, the old Phantasms are still Ethereal Magic Beings, but they're now Conjurations with souls and proper toughness.