In Standard, Reanimation decks continue to put up results
In a blog post, Wizards gave the example of Omnath, Locus of Creation, a previously banned card that will be reintroduced with an additional mana cost and an altered ability (it will now let you scry one card instead of drawing a card)
Underworld Breach can be solved with Damping Sphere, but given that Rest in Peace also gets the job done in that match-up, it earns the full four sideboard slots
It has a mini-proliferation ability, which can also help trigger its first ability again
That probably has some implications about the decision to not ban the card in February when the whole Valki-Tibalt fiasco occurred, but its not currently a disaster and WotC isnt legally obligated to keep printing more Living Ends or Glimpse of Tomorrows that would break it
[12] Even Charizard GXs weakest attack does 70 damage so its perfect for taking out weaker Pokmon