Deathstroke is a fictional DC character.
Slade Wilson luckily escaped Gotham before Scarecrow spread his fear toxin across the city. He temporarily works for Aquaman to earn some quick cash and eliminate all possible other threats that could pose as a problem.
Deathstroke appears as a boss and playable character in this crossover game between Lego Batman (hence the title) and Lego Marvel. He is hired by Hydra to assassinate Doctor Doom, but is stopped by Batman, Robin, Captain America, and Deadpool. Deathstroke is unlocked after the level (Doctor Doom Haters 6,999,999,898-7,000,000,000) is complete.