As someone who is striving to complete such missions and hasnt been lucky enough to complete more than one of them just yet, the below list of Secret Mission conditions is provided by the folk over at Pokemon Zone
Each eras design choices contribute to the games rich visual history, providing a timeline of artistic evolution that parallels the development of the game itself
And a creature-centric G/R Ramp deck With Cinder Glade really wanting a very low non-basic count (including themselves), I chose to go very lightly on them, with just two and a lone Rogues Passage
Good old Stonework Packbeast from Zendikar Rising somehow missed the changeling boat and counts as one towards your party, but no more types than is listed on the card
Theres also random needles if the dripping gore in the brain hole isnt enough for you
This is especially valuable in Gem Mint (PSA 10), which means it is virtually flawless, with perfect centering, corners, edges, and surface