If my Mishra's Factory goes to the graveyard from combat damage delivered by an opponents creature, does this trigger the Sacred Ground and return it to play?
If my opponent Diabolic Edicts me, and I sac the Factory, is Sacred Ground triggered?
No, combat damage is no effect.
Yes. Diabolic Edict is a effect.
There is a Rules Mill for something like this.
in fact this is very tricky. I dont think edict triggers sacred ground. Because it is not an effect which destroys a land, it is an effect, which make you sac a creature. This is very counter-intuitative, but I think this is the way it works.
"Whenever a spell or ability an opponent controls puts a land into your graveyard from play, return that land to play."
From the 7E text, Sacred Ground does not care how the land got to the graveyard. Thus, either Diabolic Edict or a Royal Assassin's ability would trigger sacred ground when played by an opponent. Combat damage and Shock would not.
KillerBlob Edict triggers Sacred Ground. Opponent puts land in graveyard without damage. Nuf said.