Stephen helps Chuggaaconroy demonstrate the Versus mode of Pikmin 2 on his channel. Stephen has only played the first Pikmin game, and that was a long time ago. He's rusty and Chugga is clearly the superior player. Despite this, Stephen manages to win a battle through an aggressive strategy.
Stephen (impressed): Boys and girls, that is why you marry a gamer.
Mal finds her way across a dangerous floor in Gears of War on her first try, despite not having played the game in years.
In episode 16 of the Mario Kart versus, Stephen notes that he is good at all the tracks in this cup, and in practice he beat Mal on each one. When they actually come to record, Mal proceeds to get a perfect score of 60, which requires you to take first place in every race.
The Mario Kart LP goes down to a tiebreaker after over 20 episodes ending in a tie, and in the end Mal wins.
The fact that there's almost always three Let's Plays going on at once without breaks between them.
December 2014 takes it even further by having an additional Super Smash Bros for Wii U Let's Play bringing it to four Let's Plays at once
After many fails to beat the Master Core on 7.2 Intensity, Stephen is able to beat it, with a character he's only played as twice, (Palutena).
Episode 8 of Donkey Kong Country Returns features the mine cart stages, but what takes the cake is a split path in 4-2: Since they're able to jump independently, Stephen takes a jump that leads to a background track, while Mal stays on the foreground. They're taking both routes at the same time, Stephen doesn't even lag behind.