The 'W' in "W Nebula Meteorite" most likely stands for "Worm".
The Spanish name of this card left the "W" untranslated. Furthermore, it adapted the word "nebula" to "nébula", which doesn't even exist in Spanish. The "Ally Mind" lore refered to it as "Meteoro [de la] Nébula Gusano". A correct name for this card could have been "Meteorito de la Nebulosa G" instead of "Meteorito de la Nébula W".
The Meteorite marks similarities with Leviathens from Metroid Prime 3