Abilities » Dark Aura
Does Hydreigon's "Dark Aura" Ability override the original type of attached energy, or is it in addition to the energy's original type?
Dark Aura replaces the attached energy's original type or types with Darkness type. In other words, a Fire Energy card no longer provides fire energy when Dark Aura affects it.
Source: Noble Victories FAQ (2011-11-17), PUI Rules Team (2011-11-17)
Abilities » Dark Aura
What happens to Rainbow Energy when it's attached to Hydreigon? Does "Dark Aura" Ability change it to ONLY produce Darkness Energy rather than all energy types simultaneously?
Since Dark Aura replaces the attached energy's original types with Darkness type, Rainbow Energy would lose its effect to produce all types of energy while Dark Aura is in effect. However, Rainbow Energy is still considered a "Special Energy Card" in this situation.
Source: Noble Victories FAQ (2011-11-17), PUI Rules Team (2011-11-17)