Wormfang Manta + Aminatou, the Fateshifter + Spark Double + Doorkeeper Thrull

Wormfang Manta

Aminatou, the Fateshifter

Spark Double

Doorkeeper Thrull

How it works

1. Activate Aminatou's second loyalty ability by removing a loyalty counter from it, blinking Wormfang Manta. Wormfang Manta's first ability won't trigger due to Doorkeeper Thrull
2. Wormfang Manta's second ability triggers, causing you to take an extra turn after this one.
3. Activate Spark Double's second loyalty ability by removing a loyalty counter from it, blinking Aminatou.
4. Activate Aminatou's second loyalty ability by removing a loyalty counter from it, blinking Spark Double. Choose to have Spark Double enter as a copy of Aminatou that isn't legendary.
5. Repeat each turn.

This loop achieves infinite turns by repeatedly blinking Wormfang Manta with Aminatou, the Fateshifter, letting you completely bypass the drawback of skipping your next turn thanks to Doorkeeper Thrull shutting down the Manta's enters-the-battlefield trigger. Meanwhile, Spark Double enters as a non-legendary copy of Aminatou, the Fateshifter so that the two planeswalkers can continuously blink each other and the Manta to sustain the extra turn cycle indefinitely.