When Dualcaster Mage enters the battlefield, it triggers, copying Breach the Multiverse.
Activate Phyrexian Altar by sacrificing Dualcaster Mage, adding one mana of any color.
Resolve the copy of Breach the Multiverse, causing each player to mill ten cards, then causing you to put a creature or planeswalker card from each opponent's graveyard onto the battlefield under your control, and return Dualcaster Mage from your graveyard to the battlefield.
Repeat from step 3.
Infinite colored mana.
Infinite death triggers.
Infinite magecraft triggers.
Infinite sacrifice triggers.
Put all creature and planeswalker cards from each opponent's library and graveyard onto the battlefield under your control.