When any Dragon you control attacks, you get to draw a card for each attacking Dragon and then put a permanent card from your hand into play
Heres why players love it: 1
You can even tap the Songcrafter itself to Harmonize the spell, so there will be a minimum discount of 3 lined up cunning removal from your opponents notwithstanding
Red can easily generate mana advantage as well, be it through bursty rituals (Irencrag Feat), treasure tokens (Dockside Extortionist), free spell/polymorph effects (Fires of Invention, Tibalts Trickery), or the occasional outright mana dork/discounter/mana multiplier (Leyline Tyrant, Mana Echoes)
Many of our key early-game value pieces are small artifacts, so all of these had a home here
Giving the controller of this spell full control over which permanents remain makes this significantly better than the average Wrath of God variant