I dont understand why you need finale of promise at all. Also, maybe this is only two cards
If you -2 and cast
Doublecast that starts the chain then after one doublecast resolves cast
Narset's Reversal targeting the one remaining on the stack. That will trigger the double cast of
Narset's Reversal and you can use that to continuously copy narsets.
Start Sequence
-2 from ral (let this resolve)
Stack Phase one
Doublecast (cast from hand)
Doublecast (triggered from ral)
Stack Phase two (after Doublecast triggered from ral resolves, cast narset's reversal)
Doublecast
Narset's Reversal -> targeting doublecast
Copy of Narset's Reversal triggered from Doublecast in phase one - targeting Narset's Reversal
So every resolution of the Copy of Narset's Reversal will create another copy and ral will trigger 1 damage every time.
Did I miss something?