Mentor of the Meek is particularly nice because its a three-mana creature that can be brought back with Teshar, and it will trigger off other creatures entering the battlefield from Teshar
In mill-themed builds, it does double duty by advancing your strategy while pressuring opponents from the skies
you cannot cast it without sacrificing a creature, and you cannot sacrifice additional creatures
Magic has a lot of big creatures: Krakens, Colossi, Dragons, Dinosaurs, Wurms, Eldrazi, and the list goes on
This is still a great option for a mono-green deck looking for ramp and a way to thin out the deck
Everyones list will be published, in order to minimize the advantage bigger testing teams used to get by watching lots of matches, recording data, and feeding it to others on their team