So if we follow the Atrribute criteria, we've got for choices:
DARK POSSIBLITIES:
PGD: Great Dezard, Don Zaloog, Fushioh Richie, Helpoemer, Byser Shock
MFC: Breaker the Magical Warrior, Dark Paladin
DCR: Exodia Necross, Skull Archfiend of Lightning
IOC: Strike Ninja, Dark Magician of Chaos
AST: Blowback Dragon
SOD: None
So if it all HAS to be from one Attribute, Dark is out. In fact, only three possibllities would remain:
FIRE (Horus the Black Flame Dragon LV8)
WIND (Armed Dragon LV7)
EARTH (Mystic Swordsman LV4)
since all of those are the Ultra Rare monsters from SOD.
Given those, here are the choices for promos:
FIRE
PGD: None, so FIRE and Horus the Black Flame Dragon LV8 are eliminated.
EARTH
PGD: Guardian Sphinx
MFC: Amazoness Swords Woman
DCR: Guardian Grarl
IOC: Black Tyranno
AST: Gear Golem the Moving Fortress, Ghost Knight of Jackal
SOD: Mystic Swordsman LV4
So the only guess here would be what the AST promo would be: Gear Golem the Moving Fortress or Ghost Knight of Jackal. Either way, this makes for a TERRIBLE promo set. Guardian Sphinx and Mystic Swordsman LV4 are really the only REALLY really playable cards. You could include Amazoness Swords Woman in that if you wanted.
WIND
PGD: None, so WIND and Armed Dragon LV7 are out.
So if we follow the MC1 promo "pattern" as-is (Ultra Rare monsters, all of the same Attribute), we'll be looking at a pathetic set of promos for MC2.
Even if an SOD promo is not included (maybe instead for 1 Exclusive Pack and 1 new/re-released promo) and we go on the "same Attribute" pattern in MC1, then we can rule out FIRE, WIND, and WATER based solely on PGD. Its Ultra Rare Monsters are either DARK, LIGHT, or EARTH.