The whole Running Gag of him referring to Diddy Kong as "Michael Bolton" in Diddy Kong Racing, especially since it often comes out of nowhere and gets more frequent as he goes along - to the point that towards the end he's even referring to the game title as "Michael Bolton Racing".
In particular Tehjonbro's animated version of the highlights from one episode, which depicts Pcull's monkey avatar synched to the monologue and suffering Deranged Animation as he screams "MICHAEL BOLTOOOOON!"
His Epic Fail in episode 3 of Super Mario World in which he spends ages trying to fly on a Yoshi to a platform with a key and keyhole for a secret exit, only to accidentally have the Yoshi spit the key out OVER the keyhole and lose it to the abyss below.
Throughout most of Ludwig's Castle in episode 9 he talks in a comedic German accent.
Early in episode 10, he somehow glitches out so an enemy manages to kill him while he's on Yoshi and eating the enemy. The screen immediately Smash Cuts to Pcull himself doing a Stunned Silence, so abruptly that it almost counts as a Jump Scare.
The whole Running Gag of referring to coins as "Fish Fillets".
In episode 4, Pcull's emulator randomly glitching out and turning the music into a sinister minor key at the end of a battle.
Pcull wants a Geodude for his team. He immediately finds one as soon as he enters the caves, only to accidentally kill it, and then wanders around for ages trying to find another, getting more and more infuriated as he keeps finding Zubats instead.
Having previously named one of his Pokemon 'away' (in lowercase) to make a 'Go! away!' pun, Pcull's reaction after he teaches Cut to Flarp and keeps getting the dialogue box "FLARP hacked away with CUT". "Leave away alone!"