The Fifth Doctor, and Gogo, Master of Mimicry

Prerequisites

• The Fifth Doctor on the battlefield
• Gogo, Master of Mimicry on the battlefield

Steps

1. At the beginning of your end step, The Fifth Doctor triggers
2. Holding priority, activate any number of creatures you control by tapping them, adding at least
3. Activate Gogo by paying and tapping it, copying The Fifth Doctor's trigger
4. Resolve the copy of The Fifth Doctor's trigger, untapping all creatures you control that didn't enter or attack this turn and putting a +1/+1 counter on them
5. Repeat from step 2

Results

• Infinite +1/+1 counters on all creatures you control except ones that attacked or entered the battlefield this turn
• Infinite mana creatures you control can produce except ones that attacked or entered the battlefield this turn
• Infinite untap of creatures you control except ones that attacked or entered the battlefield this turn