Osgir, the Reconstructor + Karn, the Great Creator + Ugin's Nexus + Kaya, Geist Hunter + Witch-king of Angmar

Osgir, the Reconstructor

Karn, the Great Creator

Ugin's Nexus

Kaya, Geist Hunter

Witch-king of Angmar

How it works

1. Activate Kaya's second loyalty ability by removing two loyalty counters from it, causing you to double any tokens you create this turn.
2. Activate Osgir by paying 5, tapping it and exiling Ugin's Nexus from your graveyard, creating four token copies of Ugin's Nexus.
3. Put three of the Ugin's Nexus tokens into exile due to the legend rule and their replacement effects, causing you to take three extra turns after this one.
4. Activate Karn's first loyalty ability by putting a loyalty counter on it, choosing to do nothing.
5. Move to your next extra turn.
6. Activate Kaya's first loyalty ability by putting a loyalty counter on it, giving creatures you control deathtouch until end of turn and putting a +1/+1 counter on a creature token you control.
7. Repeat from step 4 one additional time.
8. Activate Karn's second loyalty ability by removing two loyalty counters from it, returning Ugin's Nexus from exile to your hand.
9. Activate Witch-king of Angmar by discarding Ugin's Nexus.
10. Move to your last extra turn.
11. Repeat.