Equipped creature gets +1/+0.
When equipped creature deals combat damage to a player, unattach Elbrus, the Binding Blade, then transform it.
Equip 
-----Transform-----
Withengar Unbound
Legendary Creature - Demon
Flying, intimidate, trample
Whenever a player loses the game, put thirteen +1/+1 counters on Withengar the Unbound.
13/13