Picking this alternate cost means not choosing to cast the spell for its mutate cost
Each of the four Doctor Who Commander preconstructed decks features a whacky theme, according to game designer Gavin Verhey
Of course all rules need to be adjusted according to the deck as exceptions are not so rare
This doesn't seem wholly sufficient to explain the spike, otherwise why didn't it pop off during Bloomburrow, which brought in a popular new bird commander Kastral, the Windcrested
The answer is sort of three: artifacts, blue, and black
All the possible combinations are based around a roster of core decklists, however, which are also handily laid out in the blog post, along with a table explaining the 20 cards from the tabletop set being swapped for alternatives in MTG Arena, to account for the slightly different metas