Invoke Calamity a number of times equal to the number of other instants and sorceries you have cast this turn.
Resolve all but two of the copies of
Invoke Calamity and the original
Invoke Calamity, choosing not to cast any instant or sorcery spells as they resolve.
Resolve a copy of
Invoke Calamity, casting
Narset's Reversal without paying its mana cost.
Thousand-Year Storm triggers, copying
Narset's Reversal a number of times equal to the number of other instants and sorceries you have cast this turn, targeting the original
Narset's Reversal with the first copy of
Narset's Reversal and targeting the original
Invoke Calamity with all other copies of
Narset's Reversal.
Resolve a copy of
Narset's Reversal, copying the original
Invoke Calamity and returning it to your hand.
Resolve the newly copied
Invoke Calamity, choosing not to cast any instant or sorcery spells as it resolves.
Each remaining copy of
Narset's Reversal that was targeting the original
Invoke Calamity fails to resolve due to no longer having a legal target.
Resolve the copy of
Narset's Reversal targeting the original
Narset's Reversal, copying it and returning it to your hand.
Resolve the newly copied
Narset's Reversal, copying the remaining copy of
Invoke Calamity and returning it to your hand.
Resolve the copied
Invoke Calamity, casting
Invoke Calamity without paying its mana cost.
Repeat from step 2 an arbitrarily large number of times.
Once you have done so, you may choose to cast any number of instants or sorceries from your hand or graveyard with mana value six or less without paying their mana costs during step 3.
Results
Infinite copies of all instants and sorceries with mana value 6 or less in your hand and graveyard.