This is based on opinion. Please don't list it on a work's trope example list.
Tear Jerker / In The Little Wood
His killing Toby at the end of the Survival Games after Ridgedog declares there can be only one winner, is somehow both funny and depressing. First hilarious because Martyn just goes straight for him while Toby protests... and then they both go very quiet. It's been said in his livestreams that while Martyn's fully capable of backstabbing to win, he only feels bad when doing it to Toby.
Martyn once posted a video on his Vlog explaining his happy go lucky tendencies and attitude towards life. His family is one of few in the UK with a rare genetic disorder wherein their Cancer repair cells don't work, resulting in a higher propensity towards cancer, and making it impossible to survive, even with treatment. Martyn has no idea if he has the gene (he could be tested, but that would prove his mother had it, and she understandably doesn't want to know. Martyn refuses to even learn the name of the condition out of respect for her). Yeah. He basically embodies Like You Were Dying.
At this point, he has seen so many family members die of the condition that he's essentially numb to it. Finding out someone normally so positive and happy has that kind of background is pretty unnerving.
And now his mother has cancer. So far as anyone is aware, they still don't know if they have the gene. Mercifully, he later declared on Twitter that she's fine.
Any time Kaeyi is ill and the normally happy Martyn gets very angry and upset (justifiably so, of course).
After Kaeyi ended up seriously ill towards the end of September and into October 2014, Martyn mentions that he's now extremely lonely whenever she's away.
The news that he and Kaeyi have broken up. At least they're still friends.
The stream the day Martyn found out that one of his moderators had been arrested for possession of indecent images. Martyn is devastated that someone he trusted could be such a bad person. This is only exacerbated by the Mood Whiplash in the chat, where people joined with the usual "hi everyone :)" and then suddenly realised the gravity of the situation.