Breach the Multiverse by paying its mana cost, targeting any applicable target.
Holding priority, cast
Naru Meha by paying its mana cost.
When
Naru Meha enters, it triggers, targeting
Breach the Multiverse.
Holding priority, activate
Shilgengar by sacrificing
Naru Meha.
Resolve the
Naru Meha trigger, copying
Breach the Multiverse, with the copy targeting
Naru Meha.
Resolve the
Breach the Multiverse copy, returning
Naru Meha from your graveyard to the battlefield.
Repeat from step 3.
Notes
Breach the Multiverse can put all creature cards from all graveyards and libraries onto the battlefield under your control infinitely. It will also infinitely mill all players.
Results
Infinite LTB.
Infinite ETB.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite mill.
Infinite self-mill.
Put all creature cards from your library onto the battlefield.
Infinite magecraft triggers.
Infinite Blood tokens.
Infinite recursion of creature cards in your graveyard.
Put all creature cards from each opponent's library onto the battlefield under your control.