When I use Padma's F, Take one foundation from your staging area and play it as a 3 diff 3 spd mid for 3 death chaos void attack and realm of midnight is active, what happens? Nothing because it specifies no control, or is it just assumed to be a 3 like everything else?

Not three, try zero.

What Asylum said.

The attack has no specified control so it defaults to 0, so Realm of Midnight would let you play the attack at -1 difficulty.

It is a **** good thing she can only do that once per turn, or else she could run a deck with no checks that are less than 5.