Carth the Lion + Karn, the Great Creator + Ugin's Nexus + The Chain Veil + Phyrexian Altar

Carth the Lion

Karn, the Great Creator

Ugin's Nexus

The Chain Veil

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 1.
3. Ugin's Nexus triggers, causing you to take an extra turn after this one.
4. Activate The Chain Veil by paying 4 and tapping it, allowing you to activate all planeswalker abilities an extra time this turn.
5. Activate Karn's second loyalty ability by removing a loyalty counter from it, returning Ugin's Nexus from exile to your hand.
6. Move to your next turn.
7. Cast Ugin's Nexus by paying 5.
8. Repeat.