So in my campaign, the group are about to enter a grove where they hand an Elven prisoner over to some Dwarves. A Treant notices the exchange and enraged by what he sees uproots himself and charges in to deal with them.
They dont see the Treant but as they do the hand over they start to hear crashing and banging, followed by heavy footfall towards the grove, eventually the Treant bursts through the trees into the grove.
SO would it be fair to use surprise for this? or is there another rule I could use. Reason I ask is, I dont want it to be "you guys hear a load of noise and suddenly a TREANT!!!" Personally even if I heard a load of noise in the woods coming my way and then saw a Treant i'd be pretty surprised/shocked by the sight. I know surprise works by a character using a stealth attack on an unsuspecting vicitm hence the question, can I use surprise in this instance?