The fact that Sean managed to turn the Battle of Green Fork into a victory, personally fighting in the thickest of the battle, with little actual experience in fighting.
Seeing Sean manipulate half of Westeros just thanks to his foreknowledge. Best seen in the parley between Stannis and Renly, where not only does he make Renly look like an idiot, but also goads him into betting his claim to the throne in a fight between champions Sean knows is bound to go on his side.
The aforementioned champions' duel, with Loras championing Renly and Grey Wind (warged by Robb) on Ned's side. Loras loses because he trips on a peach stone (which Renly had thrown to the ground before) and Grey Wind takes advantage and mauls him.
