Enchant Boros Reckoner with mark of the vampire then get out sanguine bond, use boros charm to make it indestructible then deal damage to it from any source, continuously target itself, killing target player because of the sanguine bond.
{sanguine bond} {boros reckoner} {mark of the vampire} {boros charm}.
This combo works with anything that gives lifelink and/or indestructible.