Do Aftermath cards count as two or one card for Enigma Drake?
It becomes a 1/4.

Spring // Mind is both a sorcery card and an instant card, but it's still only one card, and Enigma Drake counts cards.

You're actually asking about split cards &mdash;the fact that they also have Aftermath is irrelevant&mdash; and the following ruling is found attached to Enigma Drake:


  A split card only counts once for Enigma Drake’s ability, even if it’s both an instant and a sorcery.