Demonic Tutor almost feels perfectly balanced in my cube in the same vein as City again being something that is played but far from whenever it can be
Your turn, your opponents turn, during combat, or in response to another spell
Blue has it unconditionally, black lets you trade life for it, green often bases it on your creatures, and red has you discard cards in exchange for a draw, but white has almost nothing
Whether you have a powered up Nykthos, Shrine to Nyx or a twice-enchanted Forest to untap, Treachery lets you grab the best creature at the table, often with a positive mana advantage
Will your opponents collaborate to deny you resources, or fall into a Nash equilibrium of selfish decisions that fill up your hand