Triumph of Saint Katherine dies, triggering itself and
Atla Palani.
Resolve the
Triumph of Saint Katherine trigger, exiling it and the top six cards of your library into a face-down pile, then shuffling that pile and putting it on top of your library.
Resolve the
Atla Palani trigger, revealing cards from the top of your library until you reveal a creature card and putting that card onto the battlefield.
Resolve the
Altar of Dementia ability from step 1, causing target player to mill cards equal to the sacrificed creature's power.
Activate
Altar of Dementia by sacrificing that creature.
Repeat from step 4 until
Triumph of Saint Katherine is on the battlefield again.
Repeat from step 1.
Results
Infinite death triggers.
Infinite ETB.
Infinite LTB.
Infinite mill.
Infinite sacrifice triggers.
Put all creatures in your library onto the battlefield, then into your graveyard.