Archaeomancer's Map Archaeomancer's Map is a great three-mana white artifact that simultaneously tutors for lands whilst providing a means of putting them into play
Silklash Spider Lets be real, reach is not the reason a card gets added to your deck (unless you're building Dhalsim, Pliable Pacifist)
Other clues will be hidden in invisible ink treatments, while the guild leaders of Ravnica, like Aurelia and Rakdos, will be featured in serialized Ravnica City cards
Rarity Cards that were printed in smaller quantities are inherently more rare and thus more collectible
It is possible, though unlikely, that the rules around vanishing will change to prevent this
For example, if an opponent controls Blood Moon, an enchantment which says Nonbasic lands are Mountains, and you play Rootpath Purifier, Blood Moon can no longer apply to the lands you control because they are all basic