Obsidian Battle-Axe

Tribal Artifact — Warrior Equipment

Equipped creature gets +2/+1 and has haste.
Whenever a Warrior creature enters the battlefield, you may attach Obsidian Battle-Axe to it.
Equip

2008-04-01:
Each of these Equipment has two subtypes listed on its type line. The first one is a creature type, which in this case is also a subtype of tribal. The second one is Equipment, which is a subtype of artifact.
2008-04-01:
Each of these Equipment has a triggered ability that says “Whenever a [creature type] creature enters the battlefield, you may attach [this Equipment] to it.” This triggers whenever any creature of the specified creature type enters the battlefield, no matter who controls it. You may attach your Equipment to another player’s creature this way, even though you can’t do so with the equip ability.
2008-04-01:
If you attach an Equipment you control to another player’s creature, you retain control of the Equipment, but you don’t control the creature. Only you can activate the Equipment’s equip ability, and if the Equipment’s ability triggers again, you choose whether to move the Equipment. Only the creature’s controller can activate any activated abilities the Equipment grants to the creature, and “you” in any abilities granted to the creature refers to that player.