Mortuary + Bolas's Citadel + Chamber Sentry

Mortuary

Bolas's Citadel

Chamber Sentry

How it works

1. Cast Chamber Sentry either from your hand by paying 0 or from the top of your library by paying 0 life.
2. Chamber Sentry enters and dies as a state-based action due to having 0 toughness.
3. Mortuary triggers, putting Chamber Sentry from your graveyard onto the top of your library.
4. Repeat.

This clever loop uses Mortuary to redirect creatures straight back to the library whenever they hit the graveyard, allowing Bolas's Citadel to cast them over and over from the top without paying actual mana. Because Chamber Sentry enters the battlefield with zero toughness when cast for zero, it instantly dies as a state-based action, which happily feeds the Mortuary trigger to set up the next iteration. You can repeat this process indefinitely to churn through your deck, racking up infinite creature enters-the-battlefield and leaves-the-battlefield triggers, as well as an arbitrarily high storm count.