Original list here:

http://www.mtgsalvation.com/forums/the-game/commander-edh/multiplayer-commander-decklists/217112-niv-mizzet-the-firemind-fireminds-fury

Potential Changes from Current List:
OUT: Worn Powerstone (worst rock)
IN: Mizzix's Mastery (OP, allows us to pitch spells and cast them for free)

Changes from Original List:
OUT: Careful Consideration (for the better spell)
IN: Dig Through Time
OUT: Counterbalance (to avoid hate)
IN: Mystic Remora
OUT: Mana Crypt (price/availability)
IN: Grim Monolith
OUT: Mox Opal (price/availability - pending MM15 reprint)
IN: Coalition Relic
OUT: Chrome Mox (price/availability - temporary)
IN: Worn Powerstone
OUT: Mana Drain (price/availability)
IN: Arcane Denial
OUT: Mindbreak Trap (not needed in my meta)
IN: Counterflux
OUT: Timetwister (lol)
IN: Time Reversal
OUT: Show and Tell (price/availability - likely OP for my meta)
IN: Trinket Mage
4/9/15
OUT: City of Brass
IN: Mana Confluence
OUT: Past in Flames
IN: Fact or Fiction
6/19/15
OUT: Mox Diamond
IN: Chrome Mox
12/11/15
OUT: Thought Reflection (expensive, no way to recur)
IN: Alhammaret's Archive (cheaper, colorless, can be recurred with Ruins)
OUT: Curiosity (boring, only good with Niv)
IN: Gilded Lotus (deck is hungry for colored mana)
12/14/15
OUT: Time Reversal (-1 wheel spell)
IN: Mystic Confluence (swiss army knife)
12/16/15
OUT: Helm of Awakening (symmetrical)
IN: Sapphire Medallion (one-sided)