Land {T}: Add {1} to your mana pool. {1}: Mishra's Factory becomes a 2/2 Assembly-Worker artifact creature until end of turn. It's still a land. {T}: Target Assembly-Worker creature gets +1/+1 until end of turn.1
Illus. Kaja & Phil Foglio
When it is an Assembly-Worker, it is still a land and retains all of its other abilities. [Duelist Magazine #2, Page 14]
When animated into an Assembly-Worker, it has creature type Assembly-Worker. [D'Angelo 2001/08/31]
The card name does not change. It remains "Mishra's Factory". [Jordan 2003/06/14]
The Assembly-Worker is an artifact creature only until the end of the turn, and then any Enchant Creature or Enchant Artifact spells on it are put into the graveyard. [Duelist Magazine #2, Page 15]
It can attack on the turn an Assembly-Worker is created, but it may not attack on the turn the land itself is brought into play. See Rule G19.39. [Duelist Magazine #2, Page 15]
Any counters on the Assembly-Worker remain even if the counters stop being meaningful when it de-animates. [D'Angelo 1998/02/03]
Tapping a land for something other than mana is not a mana ability. [D'Angelo 1999/10/01]
When it is an Assembly-Worker, it is an artifact and can therefore be affected by spells and abilities that affect artifacts, such as Disenchant. [WotC Rules Team 1995/02/09]
If another player takes control of this card while it is an Assembly-Worker, using Aladdin for example, that player keeps control until the control effect ends. They do not lose control just because the card stops being an Assembly-Worker. [WotC Rules Team 1995/02/09] Note that enchantments which steal cards (such as Control Magic and Steal Artifact) do go to the graveyard if the permanent they enchant is no longer valid.
If an Assembly-Worker is changed to another land type by something like Phantasmal Terrain, it will stay a 2/2 artifact creature and keep the creature type "Assembly-Worker" (until end of turn), but it will change its land type as directed. [Jordan 2003/06/14]
Extended tournaments (see Rule 803) have banned this card since 1999/10/01.