Grand Abolisher, Dragonlord Dromoka, Conqueror's Flail and Teferi, Mage of Zhalfir limit your opponents to casting their spells on turns other than yours (or in the case of Teferi, outside of their own)
There are many things that happen in Commander which you can copy, from Paradox Engine on the lets get silly end to just the enters-the-battlefield trigger of Solemn Simulacrum at the other
Two of them are especially siginificant to the game's lore (Urza and Mishra), but most will find a niche of their own in competitive EDH for sure
Elves are traditionally green creatures that rely on power in numbers and/or produce extra mana
It is the first time that booster packs contained 15 cards, as we know them today
Trigger Ob Nixilis with any source of 1 life loss to an opponent (e.g., attacking with a creature or a pinger)