Eris also has flying and prowess, but the most important thing is: Once it's on the battlefield, whenever you cast your second spell each turn, it creates a 4/4 red Dragon Elemental token with flying and prowess
All of these cards are nice ways to scale your decks power level to whatever your opponents are doing
Artifacts like Urzas Sylex, Nevinyrrals Disk, or Oblivion Stone warp opponents playstyles around the threat of mutually assured destruction and certainly have their place in Commander, and in the case of Sylex, tossing an extra two mana during activation to Call the Gatewatch might be just what you need to break parity following extinction
Chapter abilities are put onto the stack and may be responded to
First it immediately replaces itself drawing a card, gaining 4 puts you out of reach of Lava Spike (Omnath, Locus of Creation + Fetch Land is usually concession from Burn decks)
Giving your spells casualty doubles the value while triggering all sorts of aristocrat payoffstwo Infernal Grasps that draw a card off Morbid Opportunist sounds fantastic, but thats only the beginning
