It also works with small creature sweepers since you grow your threat without losing creatures in the process
While monstrosity allowed the creature to be cast cheaper and then evolve, prototype took a different approach, something more akin to how kicker works, where cards have two states and you can choose which version you want based on what turn it is and how much mana you have
As I mentioned at the start, though, I felt many of the other planes benefited some players more than others
Thelonite Hermit: goes with anything dropping Saproling tokens, and then goes with anything that helps with counters on your creatures or gives you benefit because you have counters on your creatures
Here, you can choose from a variety of languages available in the game
As time has gone on, though, it's been largely forgotten about and shows up very little