Sharuum the Hegemon + Phantasmal ImageInitial Card StateSharuum the Hegemon on the battlefield. StepsCast Phantasmal Image by paying 
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Phantasmal Image enters as a copy of Sharuum.
Put Sharuum into the graveyard due to the legend rule.
Phantasmal Image triggers, returning Sharuum from your graveyard to the battlefield.
Put Sharuum into the graveyard due to the legend rule.
Sharuum enters the battlefield triggers, returning itself from your graveyard to the battlefield.
Repeat from step 5.
ResultsInfinite ETBInfinite LTB