These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Badass Decay: Elec Man went from a 9/10 to a 6/10 after Roahm found out a way to completley break his AI. Averted with Bright Man, who kept his 10/10 rating even after a strategy was found that makes him less of a Luck-Based Mission. (The "revenge strategy" requires some very precise timing without charge shots)
To a lesser extent, Dragon Nezumi in the Nezumiman runs got a few points docked from his difficulty rating after Roahm discovered he has a huge blind spot.
From a non-boss standpoint, Roahm frequently used a V3 Airman chip he got early on in the Battle Network 2 LP, but he started to get less and less useful as the game progressed, to the point where he was eventually abandoned entirely.
Breather Boss: The ONLY reason why Roahm Mythril didn't give Ring Man's level a 10/10 is because of this.
He also considers Alpha from Megaman Battle Network 3 to be this so long as you have a cannon program advance in your folder.
Breather Level: In his sense, when going through an easy Robot Master after defeating a hard one (i.e. Needle Man or Quick Man)
Speaking of Quick Man, he considers MM 3 Wily Stage 1 a major example ... where he didn't even get his once. (He fought Doc Quick Man before the run).
Crowning Moment of Heartwarming: It's hard not to feel fuzzy inside whenever he shows his appreciation for his fans, and their concern when life throws him curves.
Pretty much any time he mentions his "Mum." It's obvious he regards her very fondly, and every mention of her is in reference to nostalgia and happy memories, usually of playing video games together.
Dude, Not Funny!: In Day 8 Part 4 of Mega Man Battle Network 2, "The Red-Eyed Wolly Spider?!!", Roahm clearly found the name of the titular creature ridiculously silly, so he made a Running Gag that every time the spider was mentioned, he's play a clip of his friends repeating its name in Parrot Exposition style followed by a Sting. Which would have been perfectly fine, if it wasn't accompanied by a full-screen close-up of a spider's face. Many commenters had this reaction (especially with it showing up three times over the course of the video, including as The Stinger).
Goddamned Boss: Power Piston. Roahm only gave it a 5/10 for difficulty, but found the boss long, drawn-out, and loud.
Memetic Mutation: Quite a few, the most known example is the 1-Up Curse, which makes the 1-ups to be Evil little things that want to kill you just to be useful instead of being just helpful items. (for explanation, see "Running Gag" below)
Fandom Rivalry: Averted. While Roahm admits to disliking the X series personally, he doesn't believe they're bad games, just not his type of thing. He's also one of the rare classic Mega Man fans who loves the Battle Network series.
Harsher in Hindsight: Roahm spent a good deal of time debating rather or not to take a January break to start off 2014. Then his appendix ruptures.
Hilarious in Hindsight: In the Emerald No Evolutions Run, Roahm goes on a rant that Electric types should be immune to the Static ability, saying how he hopes that's changed in a future generation. Lo and behold, Pokémon X and Ydid do this. (In fact it made Electric types immune to paralysis in general)
MST3K Mantra: Sometimes he'll point out something in the game he's playing and end it with "It's just a game, it's just a game..."
Nightmare Retardant: Silent Hill is a nightmarishly horrifying game. When Roahm LP'd it, it almost became humorous.
Tear Jerker: His aunt dying. His videos on it don't help, as they explain that he's going on hiatus due to his depression from it.
That One Boss: In the Perfect Run series, they're referred to as Nightmare Bosses. Basically, perfect 10s are guaranteed nightmares, otherwise it's whoever has the highest rating in the game.
In order of difficulty rating, the Robot Masters considered such are Enker, Strike Man, Aqua Man (7/10), Air Man, Buster Rod G, Plug Man (8/10), pre-revenge Elec Man (9/10), Needle Man, the Mega Man and Bass version of Tengu Man, Burner Man, Bright Man, Slash Man, and his original and most feared nightmare, Quick Man (10/10).
Averted with the Yellow Devil as Roahm Mythril didn't have a hard time with him (Giving Wily Stage 1 a 4/10 mostly because of the sudden enemies like the fleas and platform footholders). However, CWU-01P (The bubble boss from Wily Stage 3) was this to him, being a completely Luck-Based Mission.
The Doc Robot forms of Quick Man and Wood Man. "That hitbox, man."
He also dislikes Aqua Man from the classic series. In his words: "He really has no personality beyond 'Hi, I'm incredibly annoying!'"
Scrappy Mechanic: Escort missions ("Baggage. Yay."), Hopeless Boss Fights, and Megaman: Battle Network 3's Press program. The dragon is not particularly fond of any of these. He even calls the second of these "the cardinal sin" in Mega Man Unlimited, which ends with a "fight" against an invincible Zero.