Make sure you keep it short and attractive
But why write about it now
Players will have to factor in colored mana at some point, but that's separate from CMC
Even costing two mana and not hitting one or two drops Transgress is more effective early game disruption than Blackmail
If a powerful creature gets removed, it's not even that big of a deal thanks to how easily they can revive it or trigger one of its powerful on-death effects
(Whenever this creature becomes the target of a spell or ability an opponent controls, counter it unless that player pays 3 life.) Magecraft Whenever you cast or copy an instant or sorcery spell, create a 1/1 black and green Pest creature token with "When this token dies, you gain 1 life." Creature - Human Warlock Tinybones, Bauble Burglar Whenever an opponent discards a card, exile it from their graveyard with a stash counter on it