Umbral Mantle
Artifact — Equipment
Equipped creature has ", 
: This creature gets +2/+2 until end of turn." ( is the untap symbol.)
Equip 
It harnesses the power of night in a land where daylight fears to show itself.
Richard Sardinha
The List (PLST)
• #SHM-267Rulings
When you activate an {Q} ability, you untap the creature with that ability as a cost. The untap can't be responded to. (The actual ability can be responded to, of course.)
(wotc • 2008-05-01)
If a creature with an {Q} ability hasn't been under your control since your most recent turn began, you can't activate that ability, unless the creature has haste.
(wotc • 2008-05-01)
If the permanent is already untapped, you can't activate its {Q} ability. That's because you can't pay the "Untap this permanent" cost.
(wotc • 2008-05-01)
Rulings
When you activate an {Q} ability, you untap the creature with that ability as a cost. The untap can't be responded to. (The actual ability can be responded to, of course.)
(wotc • 2008-05-01)
If a creature with an {Q} ability hasn't been under your control since your most recent turn began, you can't activate that ability, unless the creature has haste.
(wotc • 2008-05-01)
If the permanent is already untapped, you can't activate its {Q} ability. That's because you can't pay the "Untap this permanent" cost.
(wotc • 2008-05-01)