Looking for an instant speed payoff to creatures entering or leaving the battlefield in blue/black

I'm building an Alela "flash/instant speed matters" deck thats mostly going to control the board and ping them down with fliers and incidental damage, however I want to run one combo to function as a hard wincon. To stay on theme, I want it to be able to operate at instant speed.

Right now I'm looking at [[Naru Meha, Master Wizard]] and [[saw in half]] which, with any other creature on board, can create infinite Narus. The problem is, since she's legendary, there is no way to turn the infinite Narus into a win on their own. They will die to the legend rule, so I can't untap on my turn with infinite 3/3s, however, I do have infinite triggers of creatures entering and dying the turn I do it. Unfortunately, I haven't been able to find any instant speed payoff for creatures entering or dying either. I could run a [[blood artist]] or similar, with some sort of flash enabler like [[leyline of anticipation]], but I want the combo to be 3 card or less, and flash enablers are mostly irrelevant to the rest of the deck since so much of it will already be instants or cards with flash (the only other stuff that isn't instant speed are some of the ramp and payoff effects for flash cards).

I've already done scryfall searches for everything in the color identy with flash, and instants with "whenever" or "each" (ie whenever a creature dies, or do a thing for each creature that died). So at this point I'm looking for wording that I might not have considered for an instant spell to act as a payoff for making infinite Narus, or some other infinite combo that wins the game on the spot, in blue black, thats 3 cards or less and can be done at instant speed.