Equipment, attaching, and gear that are units

Equipment is gear you attach to a unit. The unit gets the equipment's effect text and its Might bonus, and the equipment stays a separate card with its own controller, location and fate. Most questions are about what happens to that link when something changes.

Worked example. It is your Main Phase and you control Chakram Dancer (3 Might) at a battlefield. You pay Doran's Blade's Equip cost, one Body rune, an activated ability whose choice is a target (rule 818.1.b.1 and rule 818.1.c.2). The Blade attaches to the Dancer, which becomes the Top-Most Card. The Dancer now has the Blade's effect text appended and its Might changed by the Blade's Might Bonus of 2, so it has 5 Might (rule 435.1.c and rule 435.1.d). The Blade's own printed rules text is Inactive while it stays attached (rule 718.2). Because Equip is an ordinary activated ability, you cannot use it in response to your opponent's spell: it needs your own Main Phase and an Open State (rule 381).

Attaching. Equipment are still gear with all of gear's rules (rule 150.1, rule 150.2 and rule 150.4). Attaching is a Limited Action, done only when a game effect directs it (rule 435.2). Attaching to a new Top-Most Card detaches the equipment from the old one, and attaching to its current Top-Most Card does nothing (rule 435.1.f and rule 435.1.g). Attaching changes the equipment's location to the Top-Most Card's, which is not a Move, and does not change any other state: an exhausted equipment stays exhausted (rule 435.4 and rule 435.5). Only non-Unit objects can be attached, so a unit "attached" does nothing, and attached gear that becomes a unit detaches as it does (rule 435.1.h, rule 435.1.h.2 and rule 718.6.a).

Quick-Draw and Weaponmaster. Quick-Draw gives a gear Reaction and "When you play this, attach it to a unit you control" (rule 819.1.d). Weaponmaster is a play effect that lets a unit pay an Equipment's Equip cost at a discount, regardless of the usual timing, to attach it to that unit. The Equip ability is not activated and the unit with Weaponmaster is not chosen (rule 821.1.b and rule 821.1.c.6).

While attached. An attached card cannot be moved separately from its Top-Most Card (rule 718.5.c). It may have a different controller, and a change of control of one does not change the other (rule 718.5.e and rule 718.5.f). When the Top-Most Card leaves the board for a non-board zone, attached cards detach, stay on the board and take the Top-Most Card's last location (rule 719.5 and rule 436.4.b). An unattached non-Unit gear at a battlefield, or in another player's base, is recalled to its controller's base in the next cleanup, unless it has Deploy (rule 149.3, rule 459.1 and rule 830.1.b.3).

Gear that is also a unit. A game object with several types keeps the properties and permissions of all of them (rule 178.1 and rule 178.2). A gear that is also a unit has Might, can move, and is not recalled to base in a cleanup (rule 178.1.a.1 and rule 178.1.a.1.a). Effects that interact with units or with gear both apply to it (rule 178.3).

Common mistakes. "The sword dies with its carrier": it detaches and goes home. "Stealing the unit steals its equipment": it keeps its controller.