Its fun, it causes interesting interactions, and some effects even play well with the increased use of negative counters like finality and stun counters
And thus Innistrad: Crimson Vow will focus heavily on vampires and the increasing humans joining the fight to stop the endless night
But as its only one mana, it allows you to cast Isamaru on the first turn of almost every game
In the reverse, Arcbound Ravager is a nonbo with Master of Etherium and Cranial Plating
The difference is that while they have an ink cost on them, there is also an extra block of text in the description area of the card which details that you can exert a character (turning them sideways and opening them to attack) of a minimum cost in order to play the song card for free
Thankfully, these should be easier to come by, and people will be expanding their access to mana in truly exciting ways