Repeat step 1 for each other nontoken creature you control.
Cast Rise of the Dark Realms by paying ({7} magic symbol) ({B} magic symbol) ({B} magic symbol) , returning all creature cards from all graveyards to the battlefield under your control.
When Timeless Witness enters the battlefield, it triggers, returning Rise of the Dark Realms to your hand from your graveyard.
Repeat.
Results
Infinite LTB.
Infinite ETB.
Infinite colored mana.
Infinite sacrifice triggers.
Infinite death triggers.
Infinite storm count.
Infinite magecraft triggers.
Put all creature cards from all graveyards onto the battlefield under your control.