Pimpwalkin' Mateo Johnson said:
Then in what instances would using, attaching, discarding, etc. the basic versions not be acceptable, for pre-DP cards? Team Aqua's Cacturne has an attack that auto-paralyzes if you discard a Darkness Energy on TAC. Would basic Darkness Energy work in that instance?
There are no such instances
A Basic Dark would work in any instance where Dark Energy is called for. Like I said, Dark Energy is Dark Energy -- or more simply, Energy is Energy. For the example you cited, a Multi/DRE/Scramble providing Dark at the time would work as well.
If an effect
requires a Basic Energy, it will specifically say so (cf.
Magmortar SW's Flame Body Kecleon SW's Camouflage). This is the case going all the way back through the EX sets. If it doesn't restrict it to Basic Energy, any Energy card providing the required Energy will do.
The fact that EX-series cards work with the new Basic Energies is a feature. It's even advertised in the DP1 rulebook (it "adds more strategic options" for your decks
)
Pimpwalkin' Mateo Johnson said:
And while I'm asking, can Weavile's Shadow Charge fetch Dark Metal Energy, or not because it doesn't explicitly say you can (a la Dark Electrode)?
It can't fetch Dark Metal because Dark Metal only provides Dark Energy
while in play. It's just a card while in the deck.
This is the same reason you can't grab Double Rainbow, Scramble, et al. with these types of effects. If you read the Energy cards carefully, they all say they only provide their Special Energy effects while in play.
Special Dark and Special Metal are the exceptions -- if you read them, you'll notice the "while in play" qualifier is not there. They provide their respective energies at all times, including while they're in the deck.