Harmony - Troop Symmetry

Nightmares are unicorns that have changed over time due to Malassa's influence.

Apparently, the unicorns were so surprised by Malassa that their horn moved from their forehead to their nose :D

But seriously, I believe that Heroes of Might and Magic V is the most canonical (unlike the failed Heroes of Might and Magic VI and VII), and therefore, the Ashan from Heroes of Might and Magic V is the one that matters – which means that in "modern" interpretations of Ashan's creatures, there is no point if they deviate from the concept from Heroes of Might and Magic V.