#recin44

[magicjudge]

I wanted to know if Reaper of the Wilds is standard legal since it's in the V.S. Jace deck for fate reforged?

No.

Printings in supplemental products like duel decks don’t change a card’s legality.

Reaper of the Wilds has only been printed in one normal set: Theros. Theros is no longer standard legal so Reaper of the Wilds is no longer standard legal.

[magicjudge]

If I use (sacrifice) a fetch land I got from an enemy through Oblivion Sower, where does that fetch land go? I would hope it goes into my graveyard until the game was over, it would make sense that it would just no longer exist in the game, but I was told that it goes back into their graveyard! (Adding to their delve fuel?!)

It goes to its owner’s graveyard. Cards you don’t own can never be in your hand, graveyard, or library and will go to that same zone of their owner instead of doing so. If you really don’t want your opponent to be able to delve away the card, then just don’t sacrifice it.