I drafted a deck with Sonorous Howlbonder and Sea-Dasher Octopus but it won't let me mutate onto the Sonorous Howlbonder.
Sonorous Howlbonder was the only creature on the battlefield.
When I try to cast Sea-Dasher Octopus, only the creature cast option came up.
I expected to be able to mutate the Howlbonder.
Bit Error#88823 commented
That's a Human. You can't mutate onto Humans.