Rotation serves several important purposes for the health and longevity of the Pokmon TCG: Maintains a Fresh Metagame: By removing older, potentially dominant cards and strategies, rotation forces players to innovate and create new decks using the currently legal card pool
Although you'd be in mono-Black, likely with Cabal Coffers and other mana ramps, so that may not really be something you care about
All you need is one Chromatic Orrery (represented here by the best idea in this entire franchise, the Hall of Snowglobes), one self-untapping enchantment, such as Freed from the Real, and a very Christmas-friendly creature by the name of: Simply turn Chromatic Orrery into a creature using Toymaker, enchant it with Freed from the Real/Gauntlets of Light/Pemmins Aura, and HO-HO-HO, you have infinite mana of any color
That said Blackmail is much more playable than it is generally given credit for and is a fun and skill intensive card to play with too
Yes, I know it is thrilling to open them and see what is inside, but the reality is that sometimes you will only find common cards that are very difficult to trade (or not even worth using)