Basic D&D had some brilliant monsters, many of which would never make it into the "Advanced" version of the game. In truth, the Wyrd did make the jump, appearing in the Mystara Monstrous Compendium, probably because it is a really cool monster.
|"I'm so cool, I give 0 degrees Kelvin frostbite...well, that's what my mum says anyway."|
The official descriptions for these monsters say they are the corpses of elves (or aelwyn in my games), that have been reanimated by powerful undead spirits. In the canon, there are two versions, lesser and greater, the lesser not being able to paralyse with their attacks. I did away with this, and combined the two, to give a monster that is, I feel, a little more rounded. Of course, if you wanted to recreate this, you could make a version that only has one attack or the other, those throwing the Erubescent Orbs being the lesser, those throwing the Sickly Orbs, the greater.
Anyway, have fun!