Magosi, the Waterveil + Nesting Grounds + Atraxa, Praetors' Voice

Prerequisites

Magosi, the Waterveil has at least two eon counters on it. Magosi is untapped.

Steps

1. Activate Nesting Grounds's last ability by paying {1} and tapping it, moving an eon counter from Magosi to Nesting Grounds.
2. Activate Magosi's last ability by tapping it, removing an eon counter from it, and returning it from the battlefield to your hand, taking an extra turn after this one.
3. Play Magosi.
4. At the beginning of your end step, Atraxa triggers, causing you to proliferate, putting an additional eon counter on Nesting Grounds.
5. On your next extra turn, activate Nesting Grounds's last ability by paying {1} and tapping it, moving an eon counter from Nesting Grounds to Magosi.
6. Repeat from step 2.