God-Eternal Kefnet + Scroll Rack + Temporal Mastery

God-Eternal Kefnet

Scroll Rack

Temporal Mastery

How it works

1. Tap Scroll Rack and pay 1 to activate it, putting Temporal Mastery on top of your library.
2. Pass the turn.
3. On your next draw step, when you draw Temporal Mastery, reveal it due to Kefnet's ability, making a copy that costs 2 less to cast.
4. Cast the copy for 3, granting you an extra turn.