Yasova Dragonclaw
Legendary Creature — Human Warrior
Trample
At the beginning of combat on your turn, you may pay 
. If you do, gain control of target creature an opponent controls with power less than Yasova Dragonclaw's power until end of turn, untap that creature, and it gains haste until end of turn.
Winona Nelson
Fate Reforged (FRF)
• #148Rulings
The powers of the target creature and Yasova Dragonclaw are checked as you put the ability on the stack and again as the ability resolves. Once the ability resolves, it doesn’t matter what happens to either creature’s power.
(wotc • 2014-11-24)
Gaining control of a creature doesn’t cause you to gain control of any Auras or Equipment attached to it.
(wotc • 2014-11-24)
Rulings
The powers of the target creature and Yasova Dragonclaw are checked as you put the ability on the stack and again as the ability resolves. Once the ability resolves, it doesn’t matter what happens to either creature’s power.
(wotc • 2014-11-24)
Gaining control of a creature doesn’t cause you to gain control of any Auras or Equipment attached to it.
(wotc • 2014-11-24)