You can pay two mana to activate his ability and make each player Mill a card
With just two in each set, and with them being even rarer than Enchanted cards, these are likely to remain valuable for some time to come
These are powerful, and running enough of them can mitigate the need for the cards on this list, but theyre so flexible they would naturally top the list (I do have a few spells that target permanents other than artifacts, but they still say artifact)
Fira is not very fuel-efficient, but it's not bad if you consider it a bonus
The drawback of Spore Frog and Kami of False Hope is that your opponents will be able to see it coming
Adding to its value is flexibility, as the sleeve fits double-sleeve and over-sleeve cards