Magosi, the Waterveil + Rings of Brighthearth + Deserted Temple

Steps

1. Activate Magosi's second ability by paying {U} and tapping it.
2. Rings of Brighthearth triggers, choose not to pay.
3. Resolve the Magosi ability, putting an eon counter on it and causing you to skip your next turn.
4. Activate Deserted Temple's second ability by paying {1} and tapping it, untapping Magosi.
5. Activate Magosi's third ability by tapping it, removing an eon counter from it and returning it from the battlefield to your hand.
6. Rings of Brighthearth triggers, causing you to pay {2} to copy Magosi's ability.
7. Resolve both Magosi abilities, causing you to take two extra turns after this one.
8. Play Magosi.
9. Move to your first extra turn, which is skipped due to Magosi's ability which resolved in step 3.
10. Move to your second extra turn.
11. Repeat.