Unsurprisingly, I was unable to find a Trainer Deck A opening, and I refuse to open my own, but I did find an old video of a B deck opening
Since Alpha , black has been a color of explosive mana and card draw connected to loss of life
Hidden Fates, Steam Siege etc
2 Non-foil rare or mythic rare Booster fun cards from among the following: A rare (6.4%) or mythic rare (4.6%) showcase draconic frame card A rare (51.5%) or mythic rare (8.2%) borderless clan card A rare (21.5%) from among the borderless Sagas, Sieges, and lands or a borderless mythic rare Elspeth, Storm Slayer (0.7%) A rare (6.4%) or mythic rare (0.7%) borderless reversible dragon 1 Traditional foil rare or mythic rare Booster fun card from among the following: A rare (5.3%) or mythic rare (3.9%) showcase draconic frame card A rare (42.7%) or mythic rare (6.8%) borderless clan card A rare (17.8%) from among the borderless Sagas, Sieges, and lands or a borderless mythic rare Elspeth, Storm Slayer (0.6%) A rare (5.3%) or mythic rare (0.6%) borderless reversible dragon A showcase ghostfire frame card: A traditional foil ghostfire card appears 9% of the time
It was often used in decks that focused on stalling and healing
So, in summation, they are almost guaranteed to generate a "wait, what?" reaction from players should you choose to use them in-game