If Leyline of the Void is in your opening hand, you may begin the game with it on the battlefield.
If a card would be put into an opponent's graveyard from anywhere, exile it instead.
2/1/2006 Leyline of the Void affects cards that would be put into opponents’ graveyards from anywhere, not just from the battlefield.
8/15/2010 Leyline of the Void’s second ability prevents cards from ever reaching your opponents’ graveyards. Abilities that would trigger when those cards are put into an opponent’s graveyard (such as Hoarding Dragon’s last ability) won’t trigger.
8/15/2010 Leyline of the Void’s second ability doesn’t affect token permanents that would be put into an opponent’s graveyard from the battlefield. They’ll be put into that graveyard as normal (causing any applicable triggered abilities to trigger), then they’ll cease to exist.
8/15/2010 If your opponent discards a card while you control Leyline of the Void, abilities that function when that card is discarded (such as Liliana’s Caress’s ability, or a madness ability of the discarded card) still work, even though that card never reaches that player’s graveyard. In addition, spells or abilities that check the characteristics of the discarded card (such as Chandra Ablaze’s first ability) can find that card in exile.
6/8/2016 A player’s “opening hand” is the hand of cards the player has after all players have taken mulligans and “scryed” if applicable. If players have any cards in hand that allow actions to be taken with them from a player’s opening hand, the starting player takes all such actions first in any order, followed by each other player in turn order. Then the first turn begins.