Legality depends on the tournament format -- Cloud, Planet's Champion can be legal in some formats and banned or restricted in others
Threats are outpacing reactive cards significantly in terms of power level, which makes it difficult for decks like this to survive
Starting with the player whose turn it is, each player in turn order chooses up to two creatures they control, then all of the creatures not chosen by any player are sacrificed at the same time
It is important to store cards in a way that prevents them from being stacked on each other
I also put a second Olivia, Mobilized for War in the sideboard, for opponents who aren't playing Lightning Bolt, but it's possible that we'd rather have a Kalitas, Traitor of Ghet instead, for the decks that do
In other words, any time you attack youre putting a ton of pressure on your opponent where they have to choose between taking the damage or potentially giving you cards