I want to throw out a few initial sketches that can serve as starting points, because Im sure theyll need a lot of tuning to find the balance for how many of each card type and how many of each enabler and payoff are right
19 Ria Ivor, Bane Of Bladehold Battle Cry For Phyrexians Suggested Cards: Regal Bunnicorn, Elas il-Kor, Sadistic Pilgrim, Mondrak, Glory Dominus Mite tokens are very easy to flood the battlefield with, and Ria Ivor, Bane Of Bladehold, is one of the ways to accomplish this
If damage would be dealt to Bloatfly Swarm while it has a +1/+1 counter on it, prevent that damage, remove that many +1/+1 counters from it, then give each player a rad counter for each +1/+1 counter removed this way
However, I dont know what format wants to pay four mana for this effect