Mortis Engine lets you play units from other player's discard piles as if they had necromancy and were in yours. But, here's where it gets tricky.

My assumption is, Necromancy works normally, the end of the turn hits, and the unit goes back to the bottom of it's owner's deck.

But, the phrasing is a little odd. Countess Isera actually adds necromancy to the units she revives, so the text is still on the unit at the end of the turn when it travels to your deck. But, with Mortis Engine the keyword is never actually added. Reasonably this should send the card packing, but I could see an argument that because it didn't have the keyword, it should remain in play.

The other thing is, the necromancy reminder text actually specifies that the card goes to the bottom of your deck. I'm pretty sure this is supposed to go to the bottom of the owner's deck, (because shuffling another player's cards into your deck would be a nightmare) but I can't find my copy of the MotD rule insert.

"If a card would go to an out of play
zone, it goes to its owner’s out of
play zone."

(FAQ 2.2, p. 11)

The other thing isn't that clear at the moment I think, yes.

Though, I'm sure it is intended that the unit leaves play at the end of the turn. Otherwise it would/should read "You can play units from other players' discard piles as if they were in your hand."

After a little more thinking, I remembered; we do have The Liber Mortis as an example of that. "...put target unit in any discard pile into play under your control."

I couldn't find the FAQ entry though, so thanks on both counts.

Hi!
I also have a question concerning Mortis Engine:

When the selected unit leaves play at the end of the turn, does it go to its owner discard pile, or to the bottom of his deck?