Marathon commentary. Good commentary can make bad runs seem a lot better than they are, or at least a fun and enjoyable experience for everyone involved (the people watching in the room and the people watching the stream online). Bad commentary can make even good runs seem like complete disasters, even if there's nothing wrong with the run itself.
Everyone wants to have a run with good commentary, so what makes good marathon commmentary?
1. Be informative
People like to know about what's going on in the game. Speedrunners might know everything about the game being played, but when you play a game in front of 20,000+ viewers, more than a few people will have no idea what's going on. That's why explaining how the tricks work, and what they skip/how much time they save is important. Even if people who speedrun the game think the trick is simple, without any context, a lot of people won't even know that the tricks you're performing save time and/or let you skip parts of the game. People also like to know trivia, whether it's facts about the game's development, or the history of speedrunning the game. The more viewers know about the game you're playing, the more engaged they are.
2. Stay positive.
I know this message sounds like one of those bad motivational posters you saw in school as a kid, but it's true. The attitude a runner has while playing a game has a big influence on how people perceive a run, and can be the difference between a good and bad run, irregardless of how well the runner plays.
A good example of a run where the runner stayed positive despite being a bad run was Cosmo's Ocarina of Time run during SGDQ 2013. The time on the run, 26:34, is over 7 minutes slower than the current record. Cosmo was out of practice and it showed throughout the run, yet people liked the run, but why? That's because Cosmo was informative and still kept a positive attitude throughout the run, he wasn't beating himself up and he was still describing tricks in the run, even as he was failing them. Cosmo's upbeat attitude made a bad run seem like a good one.
An example of a run where commentary can make the run worse is Carcinogen's Resident Evil Code Veronica at SGDQ 2013. Was it the worst run? Gameplay-wise, no it wasn't, but Carcinogen's commentary made the run seem worse than it was. He dwelled on the bad points of the run and didn't describe how running the game worked, so the only thing to focus on was how the run wasn't going his way, which made it awkward for people in the room and did not leave a good impression on viewers.
What's worse about being negative about your own run is that it tends to start a cycle of negativity that's hard to escape. When you screw up, you focus on your mistakes, and then you start to screw up more because you're still focused on your mistakes.
3. Just be yourself.
Puwexil and Cosmo are not going to reach the hype and energy levels of Bonesaw, but they don't need to because their commentary style is a more calm and informative approach, and it's a very effective style for both of them. In fact, it would be very strange to see Puwexil and Cosmo be very energetic and hyper (I'm still waiting for a Puwexil SMAAAAAAASH!), and why should they be hyper? It's not their style, and it would seem unnatural if they tried a more animated, energetic approach. They're more about a laid back, relaxed and informative style, which works for them.
Everyone has their own style of commentary, and the best way to discover your style of commentary is to stream and see what works for you. No one is born a good commentator. If you watch marathon videos from Classic Games Done Quick to Summer Games Done Quick 2013, you will notice the commentary has improved considerably in the last three years because streaming and commentating alongside your run is much more commonplace, and people have become used to it.
P.S. Credit goes to Carcinogen and Cosmo for letting me use their runs as examples for this post.