There are not enough lives on Innistrad to satisfy his thirst for retribution.

Elbrus, the Binding Blade // Withengar Unbound

Flying, intimidate, trample
Whenever a player loses the game, put thirteen +1/+1 counters on Withengar Unbound.

Flying, intimidate, trample (A creature with intimidate can't be blocked except by artifact creatures and/or creatures that share a color with it.)
Whenever a player loses the game, put thirteen +1/+1 counters on Withengar Unbound.

Those who grasp its hilt soon hear the demon's call.

Equipped creature gets +1/+0.
When equipped creature deals combat damage to a player, unattach Elbrus, then transform it.
Equip {1}

The List

From the Vault: Transform

Equipped creature gets +1/+0.
When equipped creature deals combat damage to a player, unattach Elbrus, the Binding Blade, then transform it.
Equip {1}

Dark Ascension

Elbrus will transform even if you are unable to unattach it (most likely because the equipped creature died).

In a multiplayer game using the limited range of influence option (such as a Grand Melee game), if a spell or ability says that you win the game, it instead causes all of your opponents within your range of influence to lose the game. This is another way by which Withengar's ability can trigger.

The "legend rule" checks only for permanents with exactly the same name. Elbrus, the Binding Blade and Withengar Unbound can be on the battlefield at the same time without either going to its owner's graveyard.

Withengar's triggered ability will trigger no matter how a player loses the game: due to a state-based action (as a result of having a life total of 0 or less, trying to draw a card from an empty library, or having ten poison counters), a spell or ability that says that player loses the game, a concession, or a game loss awarded by a judge.