Animate Dead by paying ({1} magic symbol) ({B} magic symbol) , targeting
Karmic Guide in your graveyard.
Animate Dead triggers, returning
Karmic Guide to the battlefield.
Karmic Guide triggers, returning
Cavalier of Dawn from your graveyard to the battlefield.
When
Cavalier of Dawn enters, it triggers itself, targeting nothing.
Activate
Phyrexian Altar by sacrificing
Karmic Guide, adding ({B} magic symbol) .
Animate Dead is put into your graveyard as a state-based action.
Activate
Phyrexian Altar by sacrificing
Cavalier of Dawn, adding ({B} magic symbol) .
Cavalier of Dawn's last ability triggers, returning
Animate Dead from your graveyard to your hand.
Repeat.
Notes
Optionally, you may use
Cavalier of Dawn's ETB ability infinite times, destroying any number of nonland permanents and giving their controllers a 3/3 Golem for each one destroyed.