Sphinx of the Second Sun and Aggravated Assault on the battlefield.
Lands you control can tap to produce at least ({6} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Steps
Move to your postcombat main phase.
Sphinx of the Second Sun triggers, causing you to get an additional beginning phase after this phase.
Activate all lands you control by tapping them, adding at least ({6} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) ({R} magic symbol) .
Activate Aggravated Assault by paying ({3} magic symbol) ({R} magic symbol) ({R} magic symbol) , causing you to untap all creatures you control and to get an additional combat and main phase after this one.
Repeat step 4 one additonal time.
Move to the main phase from step 5.
At the beginning of the main phase, Sphinx of the Second Sun triggers, causing you to get an additional beginning phase after this phase.
Move to the beginning phase from step 7, causing you to untap all lands you control and draw a card.
Move to the main phase from step 4.
Repeat from step 2.
Results
Infinite card draw.
Infinite draw triggers.
Near-infinite combat phases.
Near-infinite untap of creatures and lands you control.