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
Results
Infinite colored mana
Infinite ETB
Infinite LTB
Infinite death triggers
Infinite sacrifice triggers
Infinite magecraft triggers
Infinite mill
Infinite self-mill
Put all creature and planeswalker cards from each opponent's library and graveyard onto the battlefield under your control