Rakdos, the Showstopper

All of the creatures whose coins come up tails are destroyed at the same time.

Players can't take any action between the time that coins are flipped and the time creatures are destroyed. For example, if they wish to cast a spell to have a creature gain indestructible, they must do so before Rakdos's triggered ability resolves, without knowing whether that creature's coin will come up heads or tails.