2017-03-14 : Boros Reckoner’s first ability will trigger even if it is dealt lethal damage. For example, if it blocks a 7/7 creature, its ability will trigger and Boros Reckoner will deal 7 damage to the target.

2017-03-14 : Damage dealt by Boros Reckoner due to its first ability isn’t combat damage, even if it was combat damage that caused that ability to trigger.

2017-03-14 : If Boros Reckoner is dealt damage by multiple sources at once, such as by two creatures blocking it, its ability triggers once and one target is dealt that much damage.