You have a way to increase only Atla's toughness by at least one
Steps
Increase Atla's toughness by at least one
Activate
Mirror Entity an arbitrarily large number of times by paying a total of ({0} magic symbol)
Resolve the first
Mirror Entity ability, causing all creatures you control to have base power and toughness 0/0 and gain all creature types until end of turn
All creatures you control except Atla die as a state-based action due to having zero toughness
If
Kozilek died this way, it triggers, shuffling your graveyard into your library
Atla triggers once for each creature that died
Resolve the first Atla trigger, revealing cards from the top of your library until you reveal a creature card, then putting the creature card onto the battlefield and all other revealed cards on the bottom of your library