Activate Chainer by discarding a card, allowing you to cast a creature spell from your graveyard this turn.
Cast Sidisi from your graveyard by paying ({3} magic symbol) ({B} magic symbol) ({B} magic symbol) .
When Sidisi enters the battlefield, its exploit ability and Chainer trigger.
Resolve the Chainer trigger, giving Sidisi haste until end of turn.
Resolve the Sidisi trigger, causing you to sacrifice Sidisi.
Sidisi's second ability triggers, causing you to search your library for Beacon of Tomorrows and put it into your hand.
Cast Beacon of Tomorrows by paying ({6} magic symbol) ({U} magic symbol) ({U} magic symbol) , causing you to take an extra turn after this one and shuffle Beacon of Tomorrows into your library.