While affinity for artifacts is the mechanic most will instantly think of when plotting how best to maximize the potential of Energy Tap, there are plenty of other creatures in and outside of blue that can easily be played for a steep discount
Since Thassas Oracle and Jace, Wielder of Mysteries dont exist in Standard, were instead interested in trying to mill out the opponent, instead
If you just want to be able to play, this is a great buy
However, Dark-type decks have their own option, as Janine's Secret Art can attach energy from the deck while also making use of the poison status effect
You need three energy to use this ability, but that's less than some of the best Pokmon TCG Pocket moves - in particular Mewtwo Ex's or Charizard Ex's devastating attacks
Like the black-and-white cards from the Twisted Toons drop, these are much more fun than just having one super-rare chase card