So, I'm playtesting two of my decks, (yeah, I do that... I need friends...) and I'm confused about how the effects of my opponent's cards that come under my control (via cards such as Act of Treason, or Mind Control), which say "you and "your," would affect me and my opponent. The specific card in question is Yavimaya Elder, which I gained control of for the turn using Act of Treason. I plan to attack with it, then sacrifice it. But the card says: "When Yavimaya Elder is put into a graveyard from the battlefield, you may search your library for up to two basic land cards, reveal them, and put them into your hand. If you do, shuffle your library." (emphasis added)
I understand that as I sacrifice the card, it would go into my opponent's graveyard, as he owns it (I know that he is me since I'm playing myself, but for all intents and purposes, "he" refers to the player of the deck who owns Yavimaya Elder). However, since the card doesn't specify "your graveyard," does that mean that it's effects that say "you" would apply to me, as Act of Treason causes me to control it until end of turn?
So my main question is, would I, owner of Act of Treason, search my library for two lands, or would my opponent, owner of Yavimaya Elder, search "his" library for two lands??