Also has access to Colossal Slam, which does heavy AoE damage (wipes shadows) and inflicts Zombie status for a short time.
If you are worried about dying, it is safest to kite until this status wears off.
Mercurial Strike does an amount of damage between 111 and 1111. The particular amount of damage it does determines what will happen next, similar to a Corsair roll:
It is recommended to kite if you are hit with a 1111 damage Mercurial Strike. If you fight at max range and start running soon enough, he will not be able to land any Colossal Slams on you.
Be careful that you do not run more than 30' away, as this will force you to disengage and likely turn Briareus white.