With both of these creatures, attacking opponents with large board states shouldnt pose much of a problem
Recently I talked about my Top 5 Clones in multiplayer formats like Commander here
(It can't be blocked, targeted, dealt damage, enchanted, or equipped by anything controlled by those players.) Fateful hour If you have 5 or less life, you can't lose life this turn, you can't lose the game this turn, and your opponents can't win the game this turn
Thats worse than the GOAT, but a bad Mayhem Devil still seems pretty impactful, especially with an ability that could turn infinite mana into infinite sacrifices into infinite damage to one target
Arbor Elf has seen a fair amount of competitive play, often alongside Utopia Sprawl