An opponent has an instant or sorcery in their graveyard.
You have a noncreature spell in hand with the mana to cast it.
Steps
Cast any noncreature spell by casting its mana cost.
Displacer Kitten triggers, blinking
Chancellor of the Spires.
When
Chancellor of the Spires enters the battlefield, it triggers, causing you to cast an instant or sorcery from an opponent's graveyard without paying its mana cost.
Repeat from step 2 for each remaining instant and/or sorcery card in each opponent's graveyard that you wish to cast.
Resolve all spells on the stack.
You may repeat this loop whenever you cast a noncreature spell.
Notes
You can start this loop by casting
Chancellor of the Spires and resolving its ETB ability instead, and then follow the above instructions for every subsequent loop.
Results
Near-infinite magecraft triggers.
Near infinite ETB.
Near infinite LTB.
Near infinite storm count.
Near-infinite casts of instant and sorcery cards in opponents' graveyards.