Turning creatures face up is a special action you can take whenever you have priority, so you can attack with your creatures face down and turn them up after blockers are declared
If you just want a clean, straightforward one-turn kill, Chandra's Ignition is a pretty good option, able to smite every creature and player in such dramatic fashion that they probably won't really mind
In a casual format like Commander where people like to play with big, splashy cards and fun creatures, an enchantment like Humility can completely turn the game on its head with a powerful effect that nerfs most commanders and popular creature cards into oblivion
But in that niche it can do some cool tricks
Digital-only cards have a big implication for MTG: Wizards of the Coast is not interested in maintaining parity with the paper version of the game anymore
Murderous Redcap: needs no introduction