Genji Glove

The extra combat step is the loud part, but the untap clause is what quietly closes the hole every extra-combat effect before it left open. The lineage of "attack again" cards (Aggravated Assault, Combat Celebrant, and their kin) has always been priced against the risk of tapping out for a second swing that strands you on the crackback. Here the equipped creature untaps the moment attacks are declared in the first combat, so the same body that just entered the swing stands upright and ready to attack again under the additional phase. Layer double strike on top and one equipped attacker throws four instances of its power across two combats before any other creature moves. The relationship between the two costs is the balancing lever: five to cast the glove is the real outlay, and the cheaper equip cost lets a single evasive threat re-arm turn after turn, which is where the payoff concentrates. This is a build around one attacker doing all the work, not a way to spread the bonus across a wide board. The "if it's the first combat phase" guard is what keeps the loop from feeding itself: the untap and the extra phase each fire exactly once, generating one bonus combat rather than an infinite chain off its own text. Any combat past that first extra phase has to be manufactured elsewhere; the glove itself grants exactly one.