Of course this isnt really a new mechanic at all, just a reimplementation of the saga mechanic introduced with Dominaria (and later reintroduced with Theros: Beyond Death and Kaldheim)
Investment capital is limited, and the more of it you sock away, the less of it you have for quick flips and other short-term financial moves
There is another side to the story though: Postie may have spent his pocket money on a card, but for Brook Trafton, the Canadian man who pulled the card in the first place, its going to be absolutely lifechanging
#10 Planar Bridge It is finished
In a dedicated self-mill deck, this card will likely often be in the double digits for power and toughness
Her lifelink ability as a creature can help pad life totals a little bit, and when she transforms into Liliana, Defiant Necromancer, her abilities there are quite nice, especially the ultimate