The biggest issue with making slivers in a Standard set is that it needs to have a heavy sliver theme to make them playable, and the design space for slivers is relatively narrow
This is the date that all products can be purchased on, with online retailers aiming to have pre-orders with you for this date also
Metallic Mimic Here's Metallic Mimics second reprint, or the first reprint in a booster format, and it does so much for a flexible 2-drop
Zell Dincht Decks on EDHREC: 337 For several years now I've been meaning to build a Mountains-matter deck, only thwarted by (my own laziness and) the lack of good cards in the theme
Compared to some of the other mechanics first introduced in Future Sight, or even other mechanics on this list, delve isn't actually all that egregious
Fetch Lands Fetch lands like Misty Rainforest, Polluted Delta, and all the rest are essential in cEDH for building perfectly smooth mana bases