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 Phyrexian Altar by sacrificing Naru Meha, adding one mana of any color.
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 colored mana.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite magecraft triggers.
Reduce any number of target creatures' toughness to zero.