14He trained Deathstroke's daughter
Deathstroke and Dick Grayson aren’t exactly friends, but he did mentor the assassin’s daughter, Rose, once.
In Nightwing #122, Dick takes on the villainous mantle of “The Renegade” in order to infiltrate a society of supervillains.
Slade believes that Nightwing
has given up being a hero, and asks him to train Rose, knowing he would be a good teacher. Dick agrees to mentor her, but teaches her heroic values in secret. Deathstroke is suspicious that Dick is still a hero and sets up a plan to test his values.
He sets up a meeting with Superman while hiding Kryptonite with his daughter. While fighting him, she slips and falls, and regardless of having Kryptonite on her, Superman catches her.
Dick tries to use this selfless act as a last-ditch attempt to turn Rose into a hero instead of a villain, but it doesn’t work.