There are a variety of game types that the community and Wizards have created over its 30-year history, with one of the most popular currently being Commander, which forces players to have a deck at 100 cards, with one of those being their commander, a legendary creature that dictates what colors of cards they can use
Maybe someone's basement floods and some serialized cards get lost in the wreckage, never to be discovered by players
Its also quite hard to catch Rest in Peace with it this would require having Ray in the graveyard and keeping green mana up, so you could answer RIPs trigger
Instead of flickering your creatures, youll tuck them under Glorious Protector until it leaves play
see below) and adds the color black and the creature type Zombie
Id recommend it if youve got a high density of the specified creature types, or if your commander belongs to one of them