2018-03-16 : The creature that doesn’t untap during its controller’s untap step is the one that Heavy Arbalest is equipped to as that untap step begins. If a creature was tapped to activate the ability granted to it by the Arbalest, but the Arbalest is no longer equipping it, it will untap as normal.

2018-03-16 : The equipped creature is the source of both the damage ability and the resultant damage, not Heavy Arbalest. For example, if Heavy Arbalest equips a green creature, the ability can target a creature with protection from artifacts but not one with protection from green.