Originally Posted by
IcyVeins
While Vodoo Dolls is active on a tank, Gara'jal will only attack that tank, and it is not possible for the other tank to take over. However, taunting Gara'jal during this time does appear to have a limited effect: the boss will attack the off-tank for the duration of taunt, after which he will return to the main tank. This is useful in two respects.
It allows the off-tank to gain some Vengeance, greatly buffing their (and the raid's) DPS.
It allows the off-tank to "save" the main tank, should they be in danger of dying.