In a dedicated self-mill deck, this card will likely often be in the double digits for power and toughness
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)
When the mana is available Deed also finds its way into control decks, giving Oath of Druids players a way out of almost any jam while often leaving their chosen creature intact, and in the old days serving as an unexpected Tutor target that could turn the game around out of nowhere
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
The format has too much mana generation for this to be enough of a setback to be worth a removal spell
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