Talk:Dreadhorde Arcanist/@comment-68.109.161.170-20190504061137/@comment-33109274-20190504111253

Probably because the converted mana cost of Carnival//Carnage is 5.

From the MTG comprehensive rules...

708.4b ''The mana cost of a split card is the combined mana costs of its two halves. A split card’s colors and converted mana cost are determined from its combined mana cost.''

See Split Card