You have an instant or sorcery card in hand that can target a single creature.
Your life total is equal to or greater than ten times the number of opponents you have, minus two, and minus an additonal one for each poison counter your opponents have.
({8} magic symbol) ({W} magic symbol) ({W} magic symbol) plus enough mana to cast the instant or sorcery available.
Steps
Cast Storm Herd by paying ({8} magic symbol) ({W} magic symbol) ({W} magic symbol) , creating a number of 1/1 Pegasus creature tokens equal to your life total.
Cast any instant or sorcery by paying its mana cost, targeting Zada.
Zada and Venerated Rotpriest trigger.
Resolve the Venerated Rotpriest trigger, causing an opponent to get a poison counter.
Resolve the Zada trigger, copying the spell for each other creature you control, with each copy targeting a different creature.
Venerated Rotpriest triggers for each copy made this way.
Resolve the first trigger, causing an opponent to get a poison counter.
If the opponent has ten poison counters, they lose the game.