Sidisi, Undead Vizier + Helm of the Host + Beacon of Tomorrows

Sidisi, Undead Vizier

Helm of the Host

Beacon of Tomorrows

How it works

1. At the beginning of combat on your turn, Helm of the Host triggers, creating a non-legendary copy of Sidisi with haste.
2. The non-legendary Sidisi enters the battlefield, triggering its exploit ability, sacrificing itself.
3. Sidisi's second ability triggers, causing you to search your library for Beacon of Tomorrows, put it into your hand, and shuffle your library.
4. Cast Beacon of Tomorrows by paying 6, causing you to take an extra turn after this one and shuffle it into your library.
5. Repeat.