So with the MACH-IV minion from the Supersonic encounter set, is the ability meant to include allies when it…

First, we’ll note that allies cannot make basic defenses, as a basic defense requires the character to use their DEF power, which allies do not have. Second, MACH-IV’s ability will receive a small update to read: “Each character without the Aerial trait cannot defend against MACH-IV’s attacks.” With this, Aerial allies and heroes can defend against his attacks.