In this case, the spell casts once for 3 damage, then again on your next upkeep for 6
Kaldheim debuts the "foretell" mechanic
For instance: if you had three Clues, enough mana, and all the relevant cards exiled under Lazav, you could cast Cackling Counterpart targeting Lazav, hold priority before it resolves, sacrifice a Clue to trigger Lazav to transform him into Marionette Master, hold priority again, sacrifice another Clue to trigger Lazav to transform into Octavia, Living Thesis, hold priority once more, cast Armor of Shadows, let everything resolve, then sacrifice a final Clue
I was curious about cutting Nissa, Voice of Zendikar when talking to Gerry, and he said he was on the draw every Game 2, and he could see Nissa, Voice of Zednikar being better on the play