When it or another Ally enters, the Excavator mills X, where X is the number of Allies we control
That said, Rise of the Floodborn will also be a self-contained draftable experience all on its own - you can visit local game stores and crack draft boosters of this during organised events without owning any cards from The First Chapter
A common approach is TCG Low minus 10% to 15% as your baseline, with a minimum price of $0.99
Dragons of Tarkir gave us five newcomers (Dragonlord Silumgar, Dragonlord Atarka, etc.), Core Set 2019 gave us retrains of the originals (Arcades, the Strategist, Nicol Bolas, the Ravager), Strixhaven added five more as the namesakes of the different schools (Tanazir Quandrix, Beledros Witherbloom, etc.), and the five metal dragons from Baldur's Gate were also given the double creature type (Ancient Bronze Dragon, Ancient Copper Dragon, etc.)