Oathbringer

Equipped creature gets +3/+1 and has double
strike, wither, and taunt.
Equip: {4} (equip only as a sorcery.)
If the equip target is The Blackthorn, instead
of paying the equip cost, exile Oathbringer.
When Oathbringer is exiled for any reason,
place one time counter on it. When
Oathbringer has no time counters on it,
equip it to The Blackthorn, if you cannot,
exile Oathbringer.