Cast Black Sun's Twilight by paying ({5} magic symbol) ({B} magic symbol) , optionally choosing to target a creature.
Holding priority, cast Naru Meha by paying ({2} magic symbol) ({U} magic symbol) ({U} magic symbol) .
When Naru Meha enters the battlefield, it triggers, copying Black Sun's Twilight, optionally choosing to target a creature.
Holding priority, activate Altar of Dementia by sacrificing Naru Meha, causing target player to mill cards equal to Naru Meha's power.
Resolve the copy of Black Sun's Twilight, giving up to one creature -5/-5 until end of turn and returning Naru Meha from your graveyard to the battlefield.
Repeat from step 3.
Results
Infinite LTB.
Infinite ETB.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite mill.
Infinite self-mill.
Infinite magecraft triggers.
Reduce any number of target creatures' toughness to zero.