Carth the Lion + Karn, the Great Creator + Ugin's Nexus + Oath of Teferi + Phyrexian Altar

Carth the Lion

Karn, the Great Creator

Ugin's Nexus

Oath of Teferi

Phyrexian Altar

How it works

1. Activate Karn's first loyalty ability by putting two loyalty counters on it, causing Ugin's Nexus to become an artifact creature until end of turn.
2. Activate Phyrexian Altar by exiling Ugin's Nexus, adding one mana of any color.
3. Ugin's Nexus triggers, causing you to take an extra turn after this one.
4. Activate Karn's second loyalty ability by removing a loyalty counter from it, returning Ugin's Nexus from exile to your hand.
5. Move to your next turn.
6. Cast Ugin's Nexus by paying 5.
7. Repeat.